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BS IV, Module I > 3. Membranes and Transport II > Flashcards

3. Membranes and Transport II Flashcards

1
Q

Lidocaine
• Pain reliever commonly used in dental practice
• Most modern dentistry depends upon lidocaine

• \_\_\_\_ dependent \_\_\_\_ channel blockers
	○ Inhibits transmission of AP
A

voltage

Na+

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2
Q

• Nearly all the neural signals emanating from pulp are associated with ____

A

pain

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3
Q

Typical ion concentrations across the membrane in mM

These differences matter:
• Small elevations in extracellular K+ can lead to ____ and death
(and malpractice litigations if erroneous infusion)
• Rapid changes form the basis of neuronal signaling and thus thoughts & pain

	• Inside:
		○ High of \_\_\_\_
		○ Low of \_\_\_\_
		○ Low of \_\_\_\_
		○ Very low of \_\_\_\_
		○ Moderate Mg
	• Outside:
		○ Low of \_\_\_\_
		○ High of \_\_\_\_
		○ High \_\_\_\_
		○ Several orders of magnitude of \_\_\_\_ compared to intracellular
	• Differences in ion concentrations are the fundamental basis of signaling 
	• How are gradients established?
		○ NaKATPase
		○ Energy requirement to maintain differences
A 
cardiac arrest
K
Na+
Cl-
Ca++

K
Na+
Cl-
Ca++

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4
Q

Chemical driving force
Glucose crossing a permeable membrane

Chemical driving force proportional to difference in ____
Chemical driving force = -RT ln([G]i/[G]o)
Where R = gas constant, T = temperature in Kelvin and [G] = glucose concentration

A

concentration

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5
Q

Diffusion
• Chemical potential:
– Molecules diffuse from high to low concentration – Move down their ____ gradient; “Downhill”

• Electric potential:
– Opposites attract
– Cations with + charge move toward ____ charged areas
– Anions with - charge move toward ____ charged areas
– Move down their ____ gradient; “Downhill”.

Ions have both ____ and ____ gradients that must be balanced at equilibrium

A

+
electrical

electrical
chemical

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6
Q

Electrochemical driving force 1

• T0, membrane is permeable to K
	○ Cl doesn't move
	○ K diffuses from inside to outside due to \_\_\_\_ driving force
		§ Concentration gradient
A

chemical

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7
Q

Electrochemical driving force 2

	• Buildup of K on outside of membrane
	• Electrical force
		○ Net positive charge on the outside
		○ Net negative charge on inside
		○ Tries to pull positive charge back inside the cell due to \_\_\_\_ gradient, but \_\_\_\_ gradient pushes K back out
A

electrical

concentration

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8
Q

Electrochemical driving force 3

• Reach equilibrium:
	○ Driving forces are \_\_\_\_ and \_\_\_\_
		§ Neither are \_\_\_\_
A

equal
opposite
resolved

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9
Q

Electrochemical driving force 4

____ energy = -RT ln([K]i/[K]o)

____ energy = zFV

Where z = valence (K+=1),
F = Faraday constant (magnitude of electric charge per mole of electron) V = voltage

* Bigger difference in cxn results in a larger \_\_\_\_ force (the log)…
* F - number applied to the electrical \_\_\_\_…
A

chemical
electrical

chemical
charges

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10
Q

Electrochemical driving force 5

At equilibrium, sum of ____ and ____ energy for K inside equals that outside

zFVi + RT ln[Ki] = zFVo + RT ln[Ko]

A

chemical

electrical

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11
Q

Electrochemical driving force 6

LOOK AT THESE SLIDES

• \_\_\_\_  is the membrane potential where they are balanced
	○ Nernst equation
A

V

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12
Q

The Nernst equation:
The Nernst equation lets you balance the electrical and chemical driving forces for ____ ions

EK is Vm when K+ is at ____; the potential at which there is no ____ of K+ for the given intracellular and extracellular concentrations

A

permeant
equilibrium
net movement

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13
Q

The equilibrium potential for major ions differs greatly

  • EK very ____
  • ENa ____
  • ECl ____
  • ECa very ____
  • Ex is potential where ion is at ____; the major ions in a cell can’t all be at ____ at same time

If Vm=-70, which ion moves least? Most? Basis for Calcium signaling

* Real driving force on \_\_\_\_ (most opposite of +125)
* \_\_\_\_ and \_\_\_\_ barely moves
* \_\_\_\_ moves decently
A

negative
positive
negative
positive

equilibrium
equilibrium

Ca++
K+
Cl-
Na+

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14
Q

The membrane potential

A typical cell has a net ____ change, of between ____ mV to ____ mV at rest

• Measure membrane potential via \_\_\_\_
A

negative

  • 50
  • 80
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15
Q

Determining the contribution of
multiple ions

Membrane potential is always with respect to the
cell ____

How do the individual equilibrium potentials combine to determine what the potential will be?

The permeability of the membrane to different ions varies: the more permeable the ion X, the more it contributes to the ____

A

interior

membrane potential

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16
Q

What decides the contribution of each ion to the membrane potential? ____

____ equation

Remember: Cl is ____ in the equation (normal in over out)

A

Relative permeability
Goldman-Hodgkin-Katz (GHK)

inverted

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17
Q

In resting cell
K+ is the biggest influence: PK large

PNa =0.05 PK =____ PCl =0.1 Because ____>____, ____, Vm close to ____

A 
1
PK
PNa
PCl
EK
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18
Q

Ca2+ contributes very little to GHK and membrane potential because ____ low and ____ levels low

A

PCa++

absolute

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19
Q

What sets resting membrane potential?

  1. Negatively charged proteins
    - ____
  2. ____
    - maintains gradients
  3. Large ____ conductance
    - Vm near Ek

Together these enable the intracellular concentration of ions to be different from extracellular and provide a ____ membrane potential. This results in large ____ gradients that can be used to signal quickly

A

impermeable
Na+-K+ pump
K+

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20
Q

Many charges are impermeant

The presence of negative ions “stuck” ____ the cell creates a permanent force that influences the distribution of ions and water across membrane
based upon rules of electrochemical gradients and osmolarity

A

inside

21
Q

Impermant anions - equilibrium
without equality

____ a key reason that ions can be at equilibrium but concentrations differ across membrane

Ionic balance means osmotic forces would swell cells:
in reality Na/K pump also keep cells from bursting as it forces out ____ and ____ follows – net loss of 1 ion per cycle

• NAKATPase
	○ Keeps cells from \_\_\_\_ from influx of H2O
	○ Forces out Na+ in conjunction with one H2O
A

impermeant intracellular anionic proteins

Na+
water

bursting

22
Q

Primary active transport Na-K-ATPase

  • Transport of ions against gradient
  • Uses 33-70% of cell ATP - critical to function
  • Found in all animal cells
  • Electrogenic – 3 Na+/2 K+ drives a net charge across membrane but only makes membrane ____ mV more negative
  • Main role is to set up gradients
  • Also stops bursting

If block with ____, takes a while for the gradients to dissipate

* \_\_\_\_, a net negative movement across membrane
* Mainly used to set up cxn gradients
A

2-4
oubain
electrogenic

23
Q

The number of ions needed for membrane potential is relatively ____

For typical 10 μM diameter cell, excess charge for a -90 mV potential

A

small

0.002%

24
Q

The proportion of ions ____ as the diameter ____

In small axon, consistent ____ can add up

The number of charges in setting the membrane
potentials and APs is a ____ number of ions in the cell

A

increases
decreases
changes
small

25
Q

Leak K+ currents add to negative membrane potential

  • Gradients drive ____ out of cell when leak channel opens
  • (If increase ____ to an ion, Vm moves toward ____ for that ion)
  • ____ pore channels
    • Molecular identity: two-pore channels
    • Maintains ____
A 
K+
permeability
Ex
two
equilibrium
26
Q

Pump, K+ channels and thus membrane potential key to salivary gland function

• Salivary glands Different combo's of ion channels and transporters that are involved in secreting solution (Na, Cl, followed by \_\_\_\_)

The contribution of ion
channels and transporters
lead to a coordinated effect

There are many ____ channels of various types that allow us to get the membrane potential; especially the two pore channels

Other channels:
• ____ exchange
• ____
• ____ exchangers

A

H2O

Na-anion
Cl-bicarbonate
Na-H

27
Q

Summary of equilibrium and membrane potential

  • The Nernst equation tells the potential at which ions are in ____ for a given concentration – no net ____
  • The GHK equation sums the contribution of multiple ions based upon their ____ and ____
  • Membrane potential determined by ____, ____, ____ currents.
A 
equilibirum
movement
concentration
relative permeability
impermeant anions
Na/K ATPase
leak
28
Q

Key ideas on equilibrium and membrane potential

  • A small change in ion concentration makes a big change in ____
  • Osmotic pressures are ____ if water is permeable
  • If an ion X is at equilibrium, ____ = Vm
  • If Ex is not = Vm at steady state, ions are pumped against the ____ of ____ movement
  • The greater the ____ of a membrane to an ion X, the closer Vm moves to Ex
A 
membrane voltage
equal
Ex
direction
passive
relative permeability
29
Q

Ion channels

• The region through the middle contains a pore, and a response to ____ change leads to ____
changes which will gate it open.

A

voltage

allosteric

30
Q

Facilitated diffusion:

Transport across membranes with a little help from the ____

  • Many large and/or charged molecules cannot diffuse across the bilipid membrane
  • Specialized proteins aid in the crossing
  • Transport called facilitated diffusion if proteins provide a route through membrane to avoid lipid barrier

•____ transport

  • ____
  • ____
A

proteins
passive
carriers
channels

31
Q

Ion channels are protein holes in lipid membranes

____ center lets ions dissolved in an aqueous solution through the pore

____ periphery keeps channel stable in lipid membrane

A

hydrophilic

hydrophobic

32
Q

Ion channel structure

Multiple segments span the membrane ____ AAs inside lipid membrane
____ AAs on extracellular face, cytoplasmic face and make pore

Voltage gated ion channels: ____ subunits create a pore

* \_\_\_\_ TM for Na+ and K+ domains with ball and chain
* No connection in \_\_\_\_ channels
A 
hydrophobic
hydrophilic
4
6
K
33
Q

Ion channel structure

____ resolution-
can actually “see” an ion channel

Starting to correlate structure and function
identify regions involved in gating, selectivity, binding etc.

A

xray defraction

34
Q

CryoEM of TRPM1 ion channel

____ > ____ crystallography in terms of resolution

CryoEM takes these ion channels, grows lots of them, purify them,
freeze them, and can begin to see orientation through ____ and through ____ power.
• You begin to orient them and see how they go together. You also get to
see the different portions.

A

CryoEM
x-ray

EM
computational

35
Q

Key characteristics of ion channels

  1. ____: What opens and closes pore?
  2. ____: What ions go through the pore? How quickly do they ions pass through?
  3. ____: Non-conducting state after activity
  4. ____: Preventing flow of ions through pore
A

gating
permeation/selectivity
inactivation
block

36
Q

Can measure activity from a single channel with a ____

Can see activity of an individual protein
When depolarize, channels open, Na+ ions flow into cells, inward current

We can measure the opening and closing of ____ ion channels through the patch
clamp.

• You press an ____ against the cell membrane. You can get a very tight seal against the membrane which allows you to measure ion ____ flowing in and out of an ion
channel.
• You can look at a ____ ion channel here which is unique.
• If you depolarize, you can see the channels open.
• Important to understand that we can ____ different ion channels in this regard.

A

patch clamp
individual

electrode
current
single
correlate

37
Q

Gating of ion channels:
how do they open and close

Channels can be gated open using:
\_\_\_\_ messengers (phosphorylation)
\_\_\_\_ binding - tooth pain \_\_\_\_ change
A

secondary
neurotransmitter
voltage

38
Q

Channel gating – there really is an opening

Opening of
connexin 26

Addition of extracellular ____ closes channel (can see visually)

A

Ca++

39
Q

Selectivity of ion channels: how to discriminate

Not just dependent on ____; K+ vs. Na+
____ interactions with channel wall
– sometimes ____ ion gives closer fit

• Selectivity comes down to \_\_\_\_ of fit with the ion channel
	○ Tighter fit releases more \_\_\_\_ and allows it to go through
A 
size
molecular
bigger
tightness
free energy
40
Q

Ion channel selectivity obeys Nernst equation

Single channel steps – (Channel as enzyme)
Can determine which ion flows through channel by seeing the voltage at which no ____ flows (equilibrium) and using intracellular and extracellular ion concentrations to compare to EK, ENa etc..

• Change voltage via \_\_\_\_
• Change \_\_\_\_ of current steps
• More depolarized, they get larger
• Plot relationship between current and voltage = \_\_\_\_
	○ How rapidly do we get more current through ion channel based on voltage
A

current
patch clamp
magnitude
conductance

41
Q

Conductance of ion channels: how ____ can ions pass through

• Different channels let more ions through per second – bigger ____
• Rate (current jump) ____ for given channel type at given gradient
• To increase total current across membrane
increase number of channels ____ or
increase the amount of ____ each channel is open - ____

• Conductance = how rapidly ions pass through via charge/second
	○ \_\_\_\_ mechanism!
• Larger pore, but sometime its about \_\_\_\_ balance = higher conductance
• Put more in membrane, or keep them open longer
	○ Increase current
A 
quickly
current
constant
open
time
gating

time-dependent
energetic

42
Q

Channel inactivation
Ball and chain model of inactivation

Protein loop moves into region exposed when voltage gates channel open

* \_\_\_\_ charged ball is tethered to membrane, binds the pocket, thereby inactivating
* Controlling conductance in a very short \_\_\_\_
* Can be open but \_\_\_\_
A

positively
timeframe
inactivated

43
Q

Channel block

____ block movement of ions through pore

____ is very effective blocker of Na+ channels. Beware of fugu (puffer fish)

Channel closed more of the time with ____

• Inhibited \_\_\_\_ dependent \_\_\_\_ channels
• Can no longer generate AP
• \_\_\_\_ - relative of lidocaine
	○ More often the channel is closed, and is open infrequently
A

local anesthetics
tetrodotoxin (TTX)
lidocaine derivative

voltage
Na+
QX-222

44
Q

Lidocaine block of Na+ channel

  • Na channel has ____ subunits.
  • Lidocaine binds very ____ within the pocket.
  • Lidocaine fits very snugly in the pocket. Lots of this is dependent on the interactions between the ____ on the side chains of these ____ and the ____ itself.
A 
4
deeply
atoms
proteins
Lidocaine
45
Q

Schematic map of ion channels and transporters related to physiological and biological activities in tooth development.

• Ion channel mutations contributing to dental issues
• Tooth eruption: Cl, KIR, TRP
• Dentin development: Cl, TRP
• Calcium homeostasis: Ca, Cx43 (gap junction)
• pH regulation: development of enamel - dentin
• Coordinated action of \_\_\_\_ in order to develop teeth
• \_\_\_\_ in ion channels that contribute to tooth development
	○ Not just \_\_\_\_ factors
  • Ca homeostasis: there are Ca channels here.
  • pH regulation is critical to the development of the enamel. Its located in the area of the dentin.
A

ion channels
polymorphisms
behavioral

46
Q

Figure 1. Schematic image of ion channels and transporters in ameloblasts (A) and odontoblasts (B).

• Heres ameloblasts and odontoblasts.
• You can see the balance of ____.
• Odontoblasts have more complex regulation with different ____ channels.
◦ ____
• As you look at the production of the enamel and others, this ____-dependent regulation leads to the formation.

• Ion channels on \_\_\_\_
A 
ion channels
Cl
TRP-V3
pH
lysosomes
47
Q

TRP channels let + ions into odontoblasts when stretched

• TRP - \_\_\_\_ in odontoblast
• Characterize the type of \_\_\_\_ via the drugs and channel blockers
	○ In combination with \_\_\_\_
A

polarized
ion channel
genetics

48
Q

Summary - Membranes 2

  • The ____ movement of an ion across the membrane is determined by balance between ____ charges and ____ forces and calculated using the Nernst equation
  • The combined influence of individual ions is determined by their ____ and calculated using the Goldman equation
  • The membrane potential is determined by ____, the ____ and ____ channels
  • The various characteristics of ion channels determine when and how much current flows through
  • In dental structures, ____ are key in development and for responding to stimuli
A 
passive
electrical
osmotic
relative permeability
impermeant anions
NaK ATPase
leak K
ion channels

BS IV, Module I (9 decks)

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