L2 - Bioelectricity

Question 1

How can Vm be measured

Answer 1

Similar method to a patch clamp

But electrode straight through the membrane

Question 2

EC Na conc

Answer 2

150 mM

Question 3

IC Na conc

Answer 3

15 mM

Question 4

EC K conc

Answer 4

5 mM

Question 5

IC K conc

Answer 5

150 mM

Question 6

EC A- conc (anion)

Answer 6

0

Question 7

IC A- conc

Answer 7

65 mM

Question 8

How are all of these Na and K concentrations maintained

Answer 8

Na/K ATPase

Question 9

Two blockers of the Na/K ATPase

Answer 9

Digoxin

Ouabain

Question 10

When Na/K ATPase blocked what is the effect on Vm

Answer 10

Vm –> o mV

Question 11

Why is the Na/K ATPase electrogenic

Answer 11

Net loss of one +ve charge

Question 12

Contribution of K channels to the equilibrium potential

Answer 12

CONCENTRATION
Tends for K to move out, down gdt
POTENTIAL
Tends for K to move in, down gdt

Equilibrium potential
Two gradients equal no current flow

Question 13

Nernst equation

Answer 13

(61.2/z) x log [x]i / [x]o

Question 14

Nenst equation for K

Answer 14

61.2 x log (5/150)

= -90.1 mV

Question 15

Contribution of Na channels to the equilibrium potential

Answer 15

CONCENTRATION
Tends for Na to move in, down gdt
POTENTIAL
Tends for Na to move out, down gdt

Equilibrium potential
Two gradients equal no current flow

Question 16

Nernst for Na

Answer 16

61.2 x log (150/15)

= +61 mV

Question 17

Goldman equation

Answer 17

Vm = (61.2/z) = log (pna[Na]o + pk[k]o) / (pna[Na]i + pk[k]i)

Question 18

What does goldman equation determine

Answer 18

Membrane potential

Question 19

Approximate Vm

Answer 19

-70 mV

Question 20

Three movements of ions at Vm

Answer 20

Na (Ena)
K (Ek)
Na/K ATPase

Question 21

If there is a change in Vm then what else must there be a change in

Answer 21

Change in the permeability to electrogenic transport

Question 22

Describe the ion channels and movement of ions at a resting Vm

Answer 22

Many K channels are open
Many Na channels are closed
Vm –> Ek

Question 23

What happens when threshold is reached

Answer 23

Voltage gated sodium channels open and the membrane potential approaches Na Nernst

Question 24

Describe the significance of Na - Amino acid transport

Answer 24

Couple down hill transport of the Na gradient to the influx of amino acids
Cell is able to sustain a high level of Na transport whilst keeping the Vm close to resting
This is done by the opening of K channels in the membrane