Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Membrane Excitability > Jon Turner week 7-9 > Flashcards

Jon Turner week 7-9 Flashcards

1
Q

6 nov wut?

A

wutwut wtf jon

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what is the difference between pores and channels?

A

pores are always open, channels are gated.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

describe the structure of channels.

A

inner vestibule - between selectivity filter and gate

outer vestibule - outside selectivity filter.

gate

selectivity filter in the middle.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what are ion channels all made of?

A

proteins, polypeptide chains.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

describe the selectivity filter on a Na channel.

A

Short, wide pore - inner ring of DEKA (Asp, Glu, Lys, Ala) side chains - net charge: -1

Outer ring of EEMD (Glu, Glu, Met, Asp) - helps stabilizes waiting ions - net charge: -3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

describe the selectivity filter on a Ca channel.

A

Again a short, wide pore containing a ring of EEEE (Glu) side chains - net charge: -4

Outer ring of DSED (Asp, Ser, Glu, Asp) - again helps stabilizes waiting ions - net charge: -3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

describe the selectivity filter on a K channel.

A

Tube of 4 x TVGYG (Thr, Val, Gly, Tyr, Gly) - all relatively neutral residues with no side chain present in the narrow pore - weak charge

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what are the states of a channel?

A

open/closed - open state allows ion transfer.

transition - between the states this is referred to as gating.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what is gating?

A

the transition between open and closed/vice versa.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

how is generalized gating achieved?

A

Twisting, tilting or bending of subunits and trans-membrane spanning α-helices (much of α-subunit around the pore region).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

describe mechanical distortion

A

Opened by distortion of the plasma membrane (mechano-sensitive).

↑ opening induced either directly or through mechanical linkage to the cytoskeleton.

Sensory transduction in sense organs such as cochlea and skin by TRP channels. Also some “leakage” K+ and Cl- channels

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

difference between activation, deactivation and inactivation?

A

activation and deactivation are open/closed.
inactivation is permanently shut.
deinactivation is undoing of this.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

describe inactivation/deinactivation.

A

localized:
Either a region in pore wall or close to it alters conformation physically occluding the pore

Or the selectivity filter changes conformation, reducing ion transfer.

Involves a relatively short amino acid sequence.

OR particle induced:
A free intracellular region of the channel protein that plugs the pore; a.k.a. “ball and chain” gating.

Involves a relatively long amino acid sequence or subunit.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

origins of the resting K membrane permeability?

A

Julius Bernstein 1902, Halle, Germany (long before anyone knew ion channel existed! Had to wait until late 1970’s, early 1980’s)

Proposed the “membrane hypothesis”

Membrane was ion-selective for K+ and so K+ was the most likely ion to be responsible for RMP as:

  • extracellular K+ concentration was known to be low
  • indirect evidence pointed to RMP being negative

1st person to apply the Nernst equation to excitable cells:
not proved until intracellular recordings were invented.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

how did hodgkin and horowicz test the membrane hypothesis?

A

Modified EK+ by changing [K+]o

Intracellular recording from a frog muscle fibre @18°C

Record RMP at varying [K+]o
Should obey the Nernst eq.

Result:
>10mM [K+] data fitted by Nernst eq.

K+ channels contribute background ion permeability for RMP >10mM

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

how do ion channels vary in ion selectivity?

A

sign and density
+ -
2+ +

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

is selectivity relative or absolute?

A

relative.

K channels allow Na to pass, if exta/intracellular K was removed they would become Na channels.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

what is an equivalent circuit?

A

An equivalent circuits is a theoretic circuit that retains the properties of whatever is being modelled in its simplest electrical form

Associates membrane currents with specific ion channels with Eions and their conductances as well as the membrane’s capacitive properties

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

describe a battery or ion pump

A

Represents the electrochemical ion gradient - a source of electrical energy (equivalent to a power source or battery)

Batteries generates a voltage known as electromotive force (emf)

For each set of ion channels:
emfion = Eion

Force that drives Iion is the driving force or voltage relative to Eion i.e. the difference between the measured transmembrane voltage Vm and Eion:
Vm - Eion
larger driving force = larger current

Units: Volt (V)

DRAW ALL DESE OUT

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

describe conductance and resistance

A

Represents the ion channel permeability - a measure of how readily a current will pass through a material (G).

therefore opposite of resistance (R), a measure of how much the material opposes the flow of current

Assigned Units: Siemens (S) or ohm-1 (Ω-1)

Represented as a variable (left) image rather that a constant (right) image

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

what is capacitance?

A

Capacitors are devices that store charge

Capacitance is a measure of that ability

Capacitance (C) = 
stored charge(Q) / voltage(V)

Two conductors separated by a non-conductive material -dielectric/insulator
LIKE A MEMBRANE GEDDIT

Intracellular and extracellular fluid are the conductors, the membrane is the dielectric that maintains charge separation

Units: Farad (F)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

how does potential difference change the stored charge if there is capacitance in a system?

A

increase -> increase

decrease -> decrease

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

what is a capacitance current?

A

current required to charge/discharge areas adjacent to the membrane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

what determines total capacitance?

A

surface area of a cell membrane.

bigger = bigger

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

what is kirchhoffs current law?

A

Total charge flowing into a point or node must be the same as total charge leaving the point or node.

For a steady state potential this is okay, Ic = 0

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

what is the simplified equivalent circuit model?

A

Em Gm in out

DRAW IT and equations

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

at a steady state what does Igm =?

A

0

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

what is net conductance?

A

Gm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

what is net conductance associated current?

A

IGm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

at a steady state what does Vm =?

A

Vm = Em

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

describe passive responses from the membrane potential.

A

injecting a current alters the membrane potential.
has a slightly weaker response, check diagram.

current flows through the membrane.

During response, Vm no longer = RMP

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

what is Ic?

A

capacitive current

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

what is IGnet

A

net ion channel current

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

dynamics over time wut

A

wutwutinthebutt

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

what is the time constant?

A

time taken to reach change in voltage (ΔVm) = 63%

pi = C x R

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

what is Iinj?

A

Ic + IGm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

capacitance equation?

A

C = Q/V

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

relationship between rate of membrane potential change to membrane capcitance?

A

the rate of membrane potential change (for any given current) is inversely proportional to the membrane capacitance.

the greater the membrane capacitance the slower the rate of change of membrane potential (for any given current).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

impact of capacitance slide?

A

???

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

relationship between conductance and time constant?

A

↓ conductance (G) → ↑ time constant () and vice versa

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

how do voltage responses differ to membrane currents?

A

Voltage responses are going to lag behind any membrane currents!

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

how does neuromodulation act?

A

affects the resting conductance.

ie shutting K channels would increase excitability.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q

describe short or long stimuli.

A

Brief/fast current stimuli need to be much larger than long/slow ones in order for the associated voltage change to reach threshold.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

What is a voltage clamp?

A

amplifier monitors membrane voltage and then estimates and injects current necessary to maintain voltage level set by user called Vcommand using “a negative feedback system”

Purpose to measure current flow across membrane and so determine current flow and conductance of ion channels responsible for the current.

Current injected to keep voltage constant is equal but of opposite polarity to trans-membrane current being generated causing membrane potential to change any point in time.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
45
Q

what does E/V mean?

A

electromotive force/voltage

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
46
Q

what does Q mean?

A

(quantity of) charge

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
47
Q

what does I mean?

A

current Intensity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
48
Q

what is G/gamma?

A

God only knows!!!??!!

conductance.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
49
Q

What is Erev?

A

Erev is the potential at which macroscopic current flow reverses direction.

So typically, if channels highly ion selective: Erev = Eion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
50
Q

what is macroscopic current?

A

whole cell conductance x driving force

I = G (Vm - Erev)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
51
Q

benefits of looking at the macroscopic current?

A

many channels contribute to observed behaviour.

reliable

Good indication of how cell behaviour would be affected over time.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
52
Q

pioneers of the voltage clamp?

A

alan hodgkin and andrew huxley

First to describe and characterize Na+ and K+ currents in the membrane of the squid giant axon in 1950’s using an early version of the voltage clamp technique.

Hodgkin & Huxley had no pharmacological tools - replaced an active ion i.e. Na+ with a non-permeating one e.g. choline+

decrease conc of Na, less depolarisation occured on the AP.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
53
Q

describe the squid giant axon.

A

Squid giant axon - large diameter fibres found in stellar nerve up to 1mm diameter usually 500-600μm.

Coordinate water ejection from mantle cavity during swimming and escape response.

Unmyelinated axons - conduction velocity - 25m/s

depolarise from -20 –> -80 for action potential

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
54
Q

H and H basic VC circuit?

A

1: A voltage protocol to be used is set by voltage command Vcom
2: The first stage of the VC amplifier measures membrane potential Vm
3: The second stage of the VC amplifier compares Vm to the predefined Vcom protocol
4: This second stage then adjusts the current flowing to a second intracellular electrode to bring Vm equal to Vcom as quickly as possible - to nullify the current causing any difference
5: If this feedback system is fast enough then the current will match that flowing at the membrane in terms of amplitude and kinetics

?????????

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
55
Q

describe hyperpolarisation and depolarisation of a giant squid axon.

A

hyper:
Very small inward current (about -30μA/cm2) due membrane leakage conductance (K+)

depol:
Transient inward followed by a sustained outward current

transient capacitive current rapid spike at the beginning.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
56
Q

effect on giant axon by blocking Na and K?

A

K:
Reversal between +30 and +60mV

Na:
lack of inactivation on +30/60
slower onset to activation

diagrams

57
Q

H&H OG findings?

A

Fast Na+ current:

Activation range -50 to 20mV

Rapid and complete inactivation

Na+ current reversal close
to ENa+ @ +40 to +50mV

“Delayed Rectifier” K+ current:

Activation range -50 to 20mV

Slow activation, non-inactivating

K+ current reversal below activation threshold close to EK+ @ -90 to -80mV

58
Q

describe single channel recordings.

A

Microscopic
timing is not precise, length they are open can vary, they are unreliable

Usually only one or a few channels of the same type

Current flow is relatively small

59
Q

advantages of macroscopic?

A

mean of lots of microscopic gives a more accurate depiction.

60
Q

what is the equation for total membrane current?

A

I = N x Fo x i

Fo = fraction of channels open at any time

61
Q

what is the equation for total membrane conductance?

A

G = N x Fo x γ

62
Q

what happens when a system is ohmic?

A

chord = slope

as both measures pass through or can be extrapolated back to Erev.
Lienar

63
Q

graph things idk wut

A

wuwtu

64
Q

what are some atypical excitable tissues?

A

Heart
Sino-atrial node - pacemaker potential

Cardiac myocytes - ventricular action potential

Pancreas
Insulin-secreting β-cells - sensing glucose

Sense organs such as the retina
Graded responses in photoreceptors

65
Q

describe the cardiac conduction system.

A

Different regions all electrically active.

Need to coordinate timing of atrial and ventricular contractions for efficient movement of blood.

Signals initiated by spontaneously active region sino-atrial (SA) node on right atrium → ventricles.

Linked by gap junctions - small pores that link the cell membranes of one cell to the next, allow current to flow through.

66
Q

how do cardiac potentials change depending on the location?

A

Electrical activity varies depending on location and cells generating activity:

Sino-atrial (SA) and atrio-ventricular (AV) nodes - slow upstroke, little plateau

Atrial and ventricular myocytes plus Purkinje fibres - fast upstroke, long plateau.

graph makes sense

67
Q

describe the sino atrial node potential structure.

A

Phase 0: upstroke
Ca2+ current (ICa) slow depolarization - L-type Cav1.2

Phase 3: repolarization
K+ current (IK) repolarization - a combination of Kir (Kir3.1/3.4) and Kr (rapid delayed rectifier or hERG - human Ether-à-go-go related gene channels, Kv11.1)

Phase 4: pacemaker phase
If (f for “funny”) - pacemaker current (during diastole)
IT (T for “transient”) - subthreshold Ca2+ current Cav3.1
Slow rising ramp-like potential that initiates the next upstroke

Same in the atrial-ventricular (AV) node

graph it

68
Q

what is If?

A

Ifunny - not activated by deplarisation, only hyperpolarisation with a threshold between -50 to -40 mV.

Eion between -20 to -10 mV due to mixed permeability to Na+ and K+

69
Q

what underlies If?

A

HCNs - hyperpolarization activated cyclic nucleotide gated channels.
ie AMP/GMP (ATP/GTP????)
intracellular domain has the cyclic nucleotide binding site, determines the voltage dependence of the channel.
shift voltage dependence +/-

CNBD - cyclic nucleotide binding domain (cAMP/cGMP) - shifts voltage-dependence of activation to a more positive (depolarized) level.

70
Q

describe the autonomic modulation of the If in the heart.

A

Parasympathetic input - vagus nerve (Xth cranial nerve) ↓ heart rate (bradycardia)

Neurotransmitter: Acetylcholine ↓ If, ↑Kir, slows pacemaker firing rate (green) via M2 muscarinic receptors - Gi →↓cAMP

Sympathetic input - T (thoracic)1-4 spinal nerves ↑ heart rate (tachycardia)

Neurotransmitter: Noradrenaline (NA) ↑ If, speeds up pacemaker firing rate.
Mimicked by Iso - isoprenaline βA-R agonist, (red) via β1 adrenergic receptors - Gs → ↑ cAMP

71
Q

what does Gi do?

A

M2 muscarinic receptors.

inhibits adenylate cyclase and reduces intracellular cAMP levels.

72
Q

what does Gs

A

B1 adrenergic receptors.

stimulates adenylate cyclase and increases intracellular cAMP levels

73
Q

describe the ventricular myocyte action potential.

A

Phase 0: upstroke
Activation of Fast INa+ NaV1.5

Phase 1: initial rapid repolarization
Inactivation of Fast INa+ NaV1.5
Transient IK+ KV4.2/4.3 (Ito)

Phase 2: plateau phase
ICa2+ L-type CaV1.2,
IK+ slow delayed rectifier KV7.1 (Ks)

Phase 3: terminal repolarization
IK+ slow delayed rectifier KV7.1 (Ks)
IK+ rapid delayed rectifier KV11.1 (Kr - hERG)
IK+ inward rectifier Kir2.1/2.2/2.3

Phase 4: resting (flat)
IK+ inward rectifier Kir2.1/2.2/2.3

graph

74
Q

describe hERG channels

A

hERG - human homolog of Drosophila Ether-à-go-go channels.

Ether-à-go-go a mutant fruit fly:
when anaesthetised with ether their legs shake like the go-go dancers at the famous LA nightclub!

hERG channels currents unusual:

typical activation >-40mV

partial inactivation when membrane potential depolarized >0mV

rapid reversal on hyperpolarization → apparent increase in current/conductance

“paradoxical resurgent current”

75
Q

what is long QT syndrome?

A

prolonged plateau

Definition: abnormally long interval between onset of excitation and contraction of the ventricles and their subsequent relaxation

i.e. interval between depolarization (0) and terminal repolarization (3)

caused by some drugs e.g. methadone, erythromycin, haloperidol

drugs need to be tested for hERG blocking action

caused by some gene mutations (need to know??)

76
Q

how does a long QT connect to ventrical fibrillation?

A

prolonged action potential leads to early after depolarization.

this can lead to a run of spontaneous activity.

77
Q

exocrine and endocrine?

A

Exocrine – secretion of digestive enzymes by pancreatic acini

Endocrine – secretion of hormones associated with metabolism by Islets of Langerhans

78
Q

makeup of cells in the pancreas?

A

insulin secreting β(B)-cells (65-90%)

glucagon-releasing α(A)-cells (15-20%),

somatostatin-producing δ(D)-cells (3-10%)

pancreatic polypeptide-containing F(PP)-cells (1%)

79
Q

how do B cells respond to different levels of glucose?

A

low glucose levels: hyperpolarised

high glucose levels:
rhythmic depolarizations and high threshold spiking.
leads to insulin release.

80
Q

describe the mechanism by which B cells respond to glucose.

A

glucose enters cell, becomes phosphorylated, mitochondria process it via krebs cycle and produce ATP.

ATP sensitive K channel sensor for levels of ATP relative to ADP within the B cells.

As ATP levels rise functionality of K channel decreases, depolarisation due to more intracellular K.
voltage dependent Ca channels trigger, Ca enters and triggers the insulin release.

In jons words:
Glucose transported by type 2 glucose transporters (GLUT2) and phosphorylated, trapping glucose inside.

Eventually, ATP is produced in the mitochondria.

The increase in ATP:ADP ratio leads to closing of ATP-sensitive K+ channels. These contribute to RMP -70mV.

Membrane potential depolarizes under the influence of other channels contributing to resting potential.

Voltage-gated calcium channels open, allowing calcium ions (Ca2+) to enter.

  1. The increase in intracellular calcium concentration triggers the secretion of insulin via exocytosis from secretory vesicles.
81
Q

describe SUR/Kir6.2 channels

A

underpin insulin release.

Four inward rectifier K+ channel subunits - Kir6.2

associated with four regulatory sulfonylurea receptor (SUR) subunits - SUR1, an ABC (ATP-binding cassette) protein

diagram.
4 kir6.2 surrounded by 4 SUR1.

Binding of ADP to SUR1 → opening, binding of ATP to Kir6.2 → closing

sensitive to ratio of [ATP] : [ADP]

82
Q

define type II diabetes mellitus.

A

Definition: hyperglycemia due to low insulin production by -cells, or insulin receptive cells showing insulin resistance

83
Q

how can type II be treated?

A

Phamacology: first line of defence to reduce gluconeogenesis in the liver (the biguanide - metformin)

If this is insufficient, then sufonylureas used to increase insulin release. First line of defence until 1990’s

Sulfonylureas target the SUR1 subunit
e.g. tolbutamide, glibenclamide

bind to ATP-sensitive K+ channel
more in a closed state
closed state → ↑ insulin release.

84
Q

What happens if SUR/Kir6.2 have a loss of function mutation?

A

“Loss of function” mutations → depolarization → ↑ insulin secretion

highly sensitive to ATP/ADP ratio
Congenital hyperinsulinism, overproduce insulin.

e.g. mutation of Kir 6.2 - persistent hyperinsulinemic hypoglycemia of infancy (PHHI)

85
Q

What happens if SUR/Kir6.2 have a gain of function mutation?

A

“Gain of function” mutations → less sensitive to high ATP/ADP ratio → hyperpolarization → ↓ insulin secretion

Neonatal diabetes; Predisposition Type 2 diabetes

86
Q

how do photoreceptors respond to light?

A

“Resting” membrane potential depends on light intensity

↑ light → hyperpolarization

↓ light → depolarization

If the dogma is that depolarization equates to increased responsiveness then photoreceptors respond to the dark!

87
Q

describe the mechanism of photoreceptors.

A

cGMP cyclic nucleotide gated (CNG) channel

Non-selective mixed cation channel  Erev ≈ 0mV

Open when cGMP binds and closed when cGMP dissociates (unbinds!)

Intracellular ligand-gated!

In dark, cGMP levels high → CNGs open → depolarization → 0mV

In light, increased PDE ↓ cGMP → CNGs close → hyperpolarization → EK+

?????

88
Q

chemical v electrical synpase

A

chemical:

  • Molecules stored in vesicles
  • Molecules diffuse across a “gap” between cell membranes
  • Signalling: relatively slow (0.5msec)
  • Unidirectional
  • Majority of transmission in the nervous system

electrical:

  • “Holes” in adjoining cell membranes: linked by channels - gap junctions
  • Signalling: very fast - near instantaneous
  • Bidirectional
  • Relatively rare in nervous system
  • Direct electrical coupling between cells
  • ions, second messengers, metabolites
89
Q

function of chemical synapses?

A

Allow modification of nervous system function:
Neural computation - integration of many input.

Exhibit plasticity - development, learning and memory.

Act as targets for drug action - neurotransmitter synthesis, release, receptors, uptake, degradation.

90
Q

how is a neurotransmitter defined?

A
  • Synthesised and stored in the pre-synaptic neurone.
  • Released upon stimulation of that neurone in a depolarization and Ca2+ dependent manner.
  • Compound must reproduce physiological effects when applied to postsynaptic neurone.
  • Located in the appropriate region at levels sufficient to evoke physiological responses.
  • Transmitter recognition & signal transduction mechanisms (receptors etc.) associated with that postsynaptic neurone.
  • Transmitter removal mechanisms.
91
Q

types of neurotransmitters?

A

small molecules:
amino acids, amines, purines.

peptides

92
Q

examples of amino acids?

A

glycine
GABA
glutamate

93
Q

examples of amines?

A

noradrenaline
dopamine
serotonin
acetylcholine

94
Q

examples of purines?

A

ATP

adenosine

95
Q

examples of peptides?

A

endorphines

somatostatin

96
Q

what is dales principle?

A

neurones release just one transmitter at all its synapses.

not true.
This is challenged by the co-existence and release of small transmitters + peptides by interneurones.

97
Q

types of vesicles?

A

small synaptic vesicles (SSVs)

large dense cored vesicles (LDCVs)

differences on table lecture 15

98
Q

describe SSVs

A

located in synapse active zones

contain small neurotransmitters

200um Ca for release

single APs

biogenesis:
Constitutive - local vesicle recycling, transmitter synthesis and uptake

99
Q

describe LDCVs

A

location is non specific, diffuse all over cell.

contain peptides (sometimes noradrenaline)

5-10um Ca for release.

repetitive activity.

Biogenesis:
Regulated - ER-derived vesicles (no recycling), transmitter production and processing under direct genomic control

100
Q

Heuser and reese vesicle experiment?

A

Heuser and Reese - “Slam freezing” rapidly cooled on a metal block after electrical stimulation of frog neuromuscular junction

Freeze fracture electron microscopy to visualize the presynaptic membrane

Sections of presynaptic membrane take at different times after a single nerve impulse

found that:
Vesicles 40-50nm diameter,
Clear centres,
Spherical,
Could contain 1000’s of  neurotransmitter molecules.

Problem: activity leads to a massive increase in membrane surface area

Answer: Vesicle recycling

101
Q

classic vesicle cycle (brief)

A 
docking
priming
fusion/exocytosis
endocytosis
recycling
102
Q

describe docking in the vesicle cycle

A

Synaptic vesicles only dock at the active zone, active zones differ between neurones

This is adjacent to signal transduction machinery of postsynaptic membrane leading to enhanced speed and precision of signaling.

103
Q

describe priming in the vesicle cycle.

A

Synaptic vesicle “maturation” process

Vesicles made competent to release transmitter (in response to Ca2+)

Requires ATP

Conformational change in proteins that drive release

104
Q

describe exocytosis in the vesicle cycle.

A

Fusion of synaptic vesicle and presynaptic terminal membrane

Requires Ca2+

Involves Ca2+ “sensor” protein

Fusion induces exocytosis - contents discharged (diffusion)

Takes about 1msec

105
Q

describe endocytosis in the vesicle cycle.

A

Synaptic vesicle membrane is recycled by endocytosis

Involves cytoskeletal protein lattice formation (from clathryn monomers) to help pinch off membrane

Takes about 5 secs.

membrane becomes coated in a protein called clathryn
??

106
Q

describe recycling in the vesicle cycle.

A

Mechanism to conserve synaptic vesicle membrane via endosome

decoated of clathryn.

Vesicles refill with transmitter (ATP-dependent again - concentrating neurotransmitter)

107
Q

what is the alternative model of the vesicle cycle?

A

kiss and run.

Full vesicle fusion may not be required to release transmitter:

SSVs recycle intact

Not via endosomes

Neurotransmitter leaks out of small fusion pores on the membrane.

108
Q

comparison of two vesicle cycles.

A

Kiss and Run Mechanism:
Fast
Low capacity - only a few vesicles at a time
Favoured at low frequency stimulation

Classical Mechanism:
Slow
High capacity - many vesicles at a time
Favoured at high frequency stimulation

109
Q

what is v-SNARE?

A

Synaptobrevin (a.k.a. VAMP)

18kDa
Single transmembrane spanning
part of the protein is in the cytosol.

110
Q

what is t-SNARE?

A

Syntaxin
35kDa.
Single transmembrane spanning.

SNAP-25
Synaptosomal-associated protein 25.
25kDa.
Anchored to membrane by acyl chain.
functional part of protein in the cytosol.
111
Q

describe the structure of the snare proteins.

A

Synaptobrevin/syntaxin/SNAP-25 make a 1:1:1 trimeric complex.

a coiled coil quaternary structure - α-helices (two from SNAP25 green/blue)

112
Q

the role of snare proteins in docking?

A

helps attach the vesicle to the membrane

113
Q

the role of snare proteins in priming?

A

change in conformation of snare proteins, become loosely associated.
Munc 18 interacts and causes tighter bonding “zippering”.
ATP dependent.
fusion can now occur.

“zippering” - formation of the SNARE-pins

114
Q

role of snare proteins in fusion?

A

The Ca2+ sensor - synaptotagmin found on vesicles

Synaptotagmin binds to SNARE-pins in absence of Ca2+ (priming)

Synaptotagmin binds to phospholipids in presence of Ca2+

Ca2+ may cause synaptotagmin to pull vesicle into membrane (fusion)

115
Q

role of snare proteins in recycling?

A

Association of SNAREs drives docking, priming and fusion

BUT SNAREs must dissociate to allow:

  • Internalisation of empty vesicles
  • Re-docking of another vesicle

This involves NSF (N-Ethylmaleimide-sensitive factor) another ATPase.

NSF binds to SNARE-pin complex to facilitate dissociation.

116
Q

describe botulinum toxins

A

Made by the anaerobic bacterium Clostridium botulinum.

Exposure either via ingestion of infected food or by infiltration of a wound.

One of the most deadly toxins known - type A most lethal (1ng/kg)

Death by respiratory failure to paralysis of respiratory muscles

The disease produced by one or more of these toxins is known as “botulism”.

Affects peripheral nervous system: flaccid paralysis of skeletal muscle and autonomic nervous system dysfunction - BUT does not cross BBB

Clinical/cosmetic uses: convergent squint (strabismus), excessive sweating, the effects of aging!

Potency so great - no one has yet quantified the minimum concentration, or minimum number of molecules, needed to disrupt function.

Use in chemical weapons or acts of terrorism! NEEDS STRICT REGULATION!!

Botulinum toxins are a group of seven neurotoxins (designated A-G)

Made as single polypeptide -1296 amino acids (Mr 150,000)

Nicked to give two chains: a 50kDa chain disulfide linked to 100kDa chain

117
Q

structure of botulinum toxins?

A

Botulinum toxins are a group of seven neurotoxins (designated A-G)

Made as single polypeptide -1296 amino acids (Mr 150,000)

Nicked to give two chains: a 50kDa chain disulfide linked to 100kDa chain

3 functional domains:
Catalytic domain: Zinc protease

Translocation domain: allows it to cross lipid membrane

Receptor binding domain: cholinergic specificity/endocytosis

diagram it

118
Q

how does botulinum act?

A

targets t/v snares.
protease.

disrupts them, prevents release of NT.

119
Q

distribution of neurones in the brain?

A

Human CNS - 86 x 109 (Herculano-Houzel)
Glutamate ↑70% 60 x 109
GABA ↑30% 26 x 109
“Neuromodulators”

120
Q

describe excitatory NTs

A

glutamate 5C

ubiquitous (“everywhere”)
cerebral cortex → spinal cord

60-70% of all synapses

121
Q

describe inhibitory NTs

A

γ-Aminobutyric acid (GABA) 4C - cerebral cortex → brain stem

Glycine 2C - brain stem → spinal cord

20-30% of all synapses

122
Q

types of synapses in CNS?

A 
gray type I 
- asymmetric.
- “Excitatory” - associated with
L-glutamatergic synapse markers 
- spherical vesicles
gray type II 
- symmetric.
- “Inhibitory” - associated with GABAergic and glycinergic
synapse markers.
- flattened vesicles
123
Q

reversal potential?

A

no response

??

124
Q

types of NT receptors?

A

ionotropic:
receptor-ionophore complex from ligand binding
fast

metabotropic:
GPCR
membrane bound proteins linked to an intracellular G protein, hydrolyses GDP to become activated. Activates a 2nd messenger.
slow

125
Q

what are the glutamate receptors?

A

AMPA
Kainate
both homomeric or heteromeric.
antagonist - Quinoxaline-2,3-dione - NBQX

NMDA
heteromeric only - dual agonism with glycine.
NMDAR2 binds glutamate
NMDAR1 binds glycine
antagonist - 2-amino-5-phosphonopentanoate (D-AP5)

all ionotropic
Non-selective mixed cation channels.
Eion  0mV

tetramers.

126
Q

voltage dependence of fast excitatory neurotransmission?

A

at -80mv resting
AMPA does most, little NMDA

at -40mv resting
AMPA less effective, more NMDA

127
Q

voltage dependence of NMDA-R receptors?

A
  • 40 to +40 linear
  • 40 to -120 currents get smaller

removing Mg causes a linear response.

Mg show voltage dependent block of NMDA channel, blocks channel at more negative potentials.
?? rectification

128
Q

L-Glu

metabotropic glutamate types?

A

homodimers.

3 groups
groups 2 and 3 similar.

129
Q

describe mechanism of group I mGlu-Rs

A

Group 1:
link to Gq, a subunit, increase PKC levels, phosphorylation occurs, closes K channels.

Tandem 2 pore domain K+ channels (K2P) close when phosphorylated → depolarization

NMDA-R current enhanced → ↑ responsiveness

Enhanced excitability

130
Q

describe the mechanism of group II % III mGlu-Rs

A

link to Gi, inhibits adenylate cyclase decreasing PKA levels, leads to dephosphorylation or Ca channels. less functional channels.

P/Q- and N-type (CaV2.1-2) CaV channels (presynaptic) → ↓ release

L-type (CaV1.1-4) CaV channels (postsynaptic) → ↓ responsiveness

Reduced excitability

131
Q

structure of GABA?

A

2a, 2b, y subunits.
GABAB
y, a, B, a, B

selective to Cl-
Eion of -70
hyperpolarisation if RMP >-70mv

132
Q

GABA antagonists?

A

bicuculline (competitive, agonist binding site - red)

picrotoxin (Cl- channel - yellow)

133
Q

glycine antagonist?

A

Strychnine

134
Q

GABA receptor types?

A

GABA B1 and B2
need to form a dimer to be functional

B1 binds to GABA
B2 signals to G protein

135
Q

antagonist for GABA?

A

Principal antagonists: CGP35348 (competitive agonist binding site)

136
Q

agonist for GABA?

A

Principal agonist: baclofen (selective agonist)

137
Q

GABA as treatment of narcolepsy?

A

Possible target for GHB (y-hydroxybutyrate) – treatment of narcolepsy, use by athletes (↑ growth hormone ) and drug of abuse 1990’s (“liquid ecstasy”)

138
Q

targets for GABAB receptors?

A

target inward rectifier channels.
interacts with GPCR which increases GIRK channel function (K channel) through B subunit.
Gi

Postsynaptic → hyperpolarization.
Reduced excitability

Inhibit Ca channels.
direct/indirect pathways.
Gi inhibits adenylate cyclase, reduces cAMP, reduces PKA and leads to dephosphorylation of Ca channel.

P/Q- and N-type (CaV2.1 & 2.2) CaV channels (presynaptic) → ↓ release.
Reduced excitability

Membrane Excitability (7 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions