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Integrated Physiology and Pharmacology > Control of Cells > Flashcards

Control of Cells Flashcards

1
Q

What are the components that make up a cell membrane?

A 
Lipids = 42% weight
Proteins = 55% weight
Carbohydrates = 3% weight
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2
Q

What are the three categories of ion channels?

A

Carries, pumps and gated channels

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3
Q

What is the role of carriers?

A

Facilitate movement using passive diffusion
Binds ions/solutes causing a conformational change
Requires a concentration gradient

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4
Q

What is the role of pumps?

A

Use active transport to move ions against their concentration gradient

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5
Q

What is the role of gated channels?

A

Cylinder protein with a gated pore so not always open critical for physiology

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6
Q

What are the two driving forces for the movement of ions?

A

Potential (charge) and chemical (concentration)

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7
Q

What is the turnover of active transport?

A

<100/second - not very fast as molecules move down their concentration gradient and ATP has to be hydrolysed first so phosphate must be present

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8
Q

Where are sodium potassium pumps not found?

A

Red blood cells in dogs

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9
Q

What is the structure of sodium potassium atpase?

A

4 subunits - 2 alpha and 2 beta

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10
Q

What can block sodium potassium atpase?

A

Nitric oxide

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11
Q

What is meant by a secondary active transporter?

A

A carrier which relies on the activity of an ATPase in order to work eg sodium potassium atpase works to keep IC low

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12
Q

What is the turnover of a carrier?

A

10^2 to 10^3 molecules per second

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13
Q

What are the three classifications of carrier?

A

Uniporter, symporter and antiporter

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14
Q

What is the turnover of gates ion channels?

A

10^6 to 10^8 ions per second

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15
Q

Who developed the patch clamp technique?

A

Nehr and Sakman

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16
Q

What is the patch clamp technique used for?

A

To directly see or measure ion channels opening and closing in a cell

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17
Q

How is a patch clamp test carried out?

A

A glass pipette is used which contains a silver electrode and a salt solution of a known concentration
Another electrode is in an experimental bath
The glass pipette touches the back of the cell - when sucked it seals the membrane (cell attached configuration)
This allows the function of a single ion channel to be measured
If the membrane is broken the current through all channels can be measured (whole cell configuration)

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18
Q

What is the equation used to work out total current?

A 
I = N x Po x g x (Vm-Ei)
I = current
N = no. of channels
Po = open probability
g = single channel conductance
Vm = membrane potential
Ei = Equilibrium potential of ion
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19
Q

How can ion channels be regulated?

A 
Number of channels at membrane
The open probability of the channel - affected by phosphoryl, calcium and g proteins etc
The potential (Vm - Ei)
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20
Q

What is the general structure of a voltage gated potassium channel?

A

6 transmembrane spanning domains in each of the 4 subunits

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21
Q

What is the general structure of a kir protein?

A

2 transmembrane spanning domains in each of the 4 subunits

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22
Q

What is the general structure of a voltage gated sodium channel?

A

24 transmembrane spanning domains in 1 subunit

beta 1 and 2 regulate the ion channel

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23
Q

What is KcsA?

A

A bacterial K+ channel homologous to the kir mammalian family

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24
Q

How was Vm measured before the patch clamp technique was developed?

A

A glass electrode is filled with solution (1m KCl) and a silver electrode is also used with respect to zero Vm
The diameter of the tip used is much smaller than that used in patch clamping (1x 10^-6) and is very sharp
This measures Vm but does not tell us what causes it

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25
Q

What is the EC concentration of sodium?

A

150mM

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26
Q

What is the IC concentration of sodium?

A

15mM

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27
Q

What is the EC concentration of potassium?

A

5 mM

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28
Q

What is the IC concentration of potassium?

A

150mM

29
Q

What is the EC concentration of A-?

A

0mM

30
Q

What is the IC concentration of A-?

A

65mM

31
Q

What is the nernst equation?

A 
Eion = RT/zF x log [ion} out / [ion] in
R = gas constant
T = Temperature in kelvin
z = charge of ion
F = Faradays constant

Usually RT/zF = 61/Z

32
Q

What is the nernst potential for potassium?

A

-91mV

33
Q

What is the nernst potential for sodium?

A

+61mV

34
Q

What is the relative permeability of sodium?

A

1

35
Q

What is the relative permeability of potassium?

A

50-75

36
Q

What is the Goldmann’s equation?

A

Vm = 61/z x log p[Na]out + p[K]in / p[Na]out + p[K]in

37
Q

What happens if the proximal tubule is exposed to phenylalanine and why?

A

It moves towards the nernst potential as it is co transported with sodium

38
Q

Describe the ion channels in the epithelial cells lining the thick ascending limb of the loop of Henle

A 
Basolateral membrane: 
sodium potassium atpase
CLKB allows chlorine to exit cell
Apical membrane:
NKCC (sodium potassium 2 chloride)
Potassium recycling channels
39
Q

Describe the model of the sodium potassium atpase

A

1) Sodium binds to the sodium binding point
2) ATP phosphoryaltes the pump
3) Conformational change occurs so sodium leaves the cell
4) K binds to the new binding siteand dephosphorylation causes another conformational change

40
Q

What can Na/K atpase be inhibited by?

A

cardiac glycosides such as oubain and digoxin

41
Q

What is the exctracellular concentration of calcium?

A

1mM (1,000,000nM)

42
Q

What is the intracellular concentration of calcium?

A

100nM

43
Q

What is ECa?

A

+120mV

44
Q

What are the two main ways to keep intracellular calcium low?

A

Na/Ca exchanger

Ca ATPase

45
Q

How does the Na/Ca exchanger work?

A

It moves 3 sodium in for 1 calciumm out

This makes the effect of the 10 fold gradient cubed (sodium)

46
Q

What gene family is the Na/Ca exchanger part of?

A

SLC8

47
Q

What are the three types of Ca ATPases in cells?

A

PMCA - plasma membrane calcium pumps act calcium across the cell membrane
SERCA - Ca pumps found on the sarcoplasmic reticulum or endoplasmic reticulum which pump calcium out of the cytoplasm into organelles to act as calcium stores
SPCA - Ca pumps on golgi apparatus

48
Q

What are mechanically activated calcium channels?

A

Found in many cells and respond to cell deformation eg stratch activated channels

49
Q

What are the two classes of calcium channels in calcium store membranes?

A

IP3 receptors

Ryanodine receptors

50
Q

What are ryanodine receptors?

A

Receptors that respond to low concentrations of ryanodine (high concentrations inhibit? or caffeine. Tend to be found in ecxitable cells

51
Q

What is the relationship between calcium release from stores and SOCC?

A

IP3 receptor is acivated
This causes PLC (phospholipase C to be activated)
This activates PIP2
This causes calcium to be released from stores and calcium to enter the cell

52
Q

How is pH calculated?

A

pH = -log[H+]

53
Q

What could be the effects of changes in pH?

A

Change in protein charge, conformation and function

54
Q

How is pH measured using electrode?

A

Two electrodes used - V1 and V2
V1 has a sensitive H+ resin
V2 is a normal electrode and measures the potential difference of all ions whereas V1 excludes H+
The voltage difference between V1 and V2 is measured
The change in voltage is proportional to pH
Calibration with two solutions with a known pH must be done first

55
Q

Using electrodes to measure pH is suitable for which cell types?

A

Big cells, nerves, muscles or Xenopus oocytes

The electrodes are to big to use in epithelial cells

56
Q

How is pH measured using fluorescent indicators?

A

Cells are loaded with a lipid soluble inactive form of an indicator - it is converted to the active form inside the cell
The indicator is excited with light at a specific wavelength
The wavelength emitted is measured
The indicator is calibrated inside the cell. The membrane is permealised with a proton ionophore and the pH of the bath solution is changed

57
Q

What is a proton ionophore?

A

An ionophore allows the pH in and out the cell to be the same

58
Q

What are the three main ways of controlling intracellular pH?

A

Buffering
Acid extrusion
Acid loading

59
Q

How is buffering power defined?

A

The amount of strong base that must be added to a solution in order to raise the pH by a given amount

60
Q

Which channel is used in acid extrusion?

A

Na/H exchanger

61
Q

What is the role of Na/H exchangers?

A

Move Na into the cell and H+ out of the cell
Its action relies on the inward gradient of sodium
Activity is stimulated at a setpoint - this is when the pH is acidic

62
Q

Describe the allosteric modicification of Na/H exchangers

A

Protons bind to allosteric sites ( not the transport site) which leads to a conformational change which increases the activity of the protein

63
Q

NHE1 can be inhibited by what?

A

Low concentrations of amoloride and its analogue EIPA (EIPA works on sodium exchangers but not sodium channels)

64
Q

Where is NHE1 found?

A

The basolateral membrane of epithelial cells

65
Q

Which channel is used in acid loading?

A

The Cl/HCO3 exchanger

66
Q

The Cl/HCO3 exxhanger belongs to which family?

A

The AE family

67
Q

How does the Cl/HCO3 exchanger work?

A

It causes Cl to leave the cell and HCO3 to enter the cell. This works as removing HCO3 increases the relative concentration of H+ = acidification

68
Q

What are Cl/HCO3 exchangers inhibited by?

A

The AE family are all inhibited by the stilbene derivative drigs DIDs

69
Q

Where are the Cl/HCO3 exchangers found?

A

Red blood cells, some in the kidney

Integrated Physiology and Pharmacology (17 decks)

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