1 - Resting membrane potential

Question 1

Which ions has the concentration of

ICF 140mM; ECF 5mM?

Answer 1

K+

Question 2

Which ions has the concentration of

ICF 15mM; ECF 145mM?

Answer 2

Na+

Question 3

Which ions has the concentration of

ICF <0.0001 mM; ECF 1.8 mM?

Answer 3

Ca2+

Question 4

Which ions has the concentration of

ICF 7.0mM; ECF 115mM?

Answer 4

Cl-

Question 5

Cells are bathed in extracellular fluid (ECF) containing high ____ and ____ , while intracellular fluid (ICF) has high ______ balanced by ___________
, etc. to maintain electroneutrality.

Answer 5

[Na+] and [Cl-]

[K+]; protein anions [Pr-], PO4 -

Question 6

Normally, the potassium has high permeability to the K+ channels due to more _________. As K+ diffuses out downs its concentration gradient, the ICF become more and more negative since the K+ movement is not accompanied by the impermeable negative charged protein in cell.
The charge separation resulted is known as ________.

Answer 6

leak channels;

diffusion potential

Question 7

When each major ion is considered individually by assuming that the cell membrane is permeable only to that particular
ion through the leak channels. In a mammalian neuron,
• The K+ equilibrium potential (EK) is around ______.
• The Na+ equilibrium potential (ENa) is around _____.
• The Cl- equilibrium potential (ECl) is around _________.

Answer 7

-90 mV;
+60 mV;
-75 mV

Question 8

At 37 oC, what is the Nernst Equation?

E= ?

Answer 8

E = 61.5/z log [l]o/[l]i

z depends on the ion charge

e.g.
For the Nernst equation used for calculating the equilibrium potential, E equals to RT/zF * log [ion]outside /[ion]inside, and at 37C, RT/zF for monovalent ions is 61.
What is the equilibrium potential for Cl- if its intracellular and extracellular concentrations are 11 mM and 110 mM, respectively?

z = -1

Question 9

Driving force = ?

Answer 9

Vm - Eion

Vm is -70mV

therefore Driving force of Na+ =
-70 - (+60)
= -130 mV

Question 10

Which ion has the highest electrochemical driving force?

Answer 10

Ca2+

but doesn’t contribute much due to its low permeability

Question 11

What are the factors determining the generation of action potential ?

Answer 11

1. Intracellular and extracellular [K+] and [Na+] in determining their equilibrium potential
2. Difference in membrane conductance/ permeability to K+ and Na+
3. Presence of impermeable intracellular proton anions (Pr-)
4. Activity of Na+/K+ pump

Question 12

Why extracellular [K+] has a major impact on the resting membrane
potential?

Answer 12

RMP(-70mV) is closer to the equilibrium potential of K+
(-90mV) than Na+
(+60mV), because K+ has higher conductance.

Small electrochemical force is already sufficient to generate large current to counter the sodium current.

Question 13

Na+ /K+ pumps pump?

Answer 13

pumps 3Na+ out for every 2K+ into the cell, it creates unequal charge distribution

• make the RMP a little bit negative(3~5mV)

Question 14

Factor contributing the RMP and importance of it.

Answer 14

• Different ions concentration across the cell determined their equilibrium potential
• Different ions permeability determines their contribution to RMP
• Impermeable protein anion
• Activity of Na+
/K+ pump

Question 15

Factor affecting Na+

/K+-ATPase ?

Answer 15

• Blocked by Ouabain and digoxin, Hypoxia
• If blocked > Cell swelling > burst or membrane
depolarization
• B2-adrenergic effect > increases activity of the pump
by phosphorylation
• Insulin > increases recruitment of pump to cell
surface
• Thyroxine / aldosterone (principle cell of kidney) >
increases transcription of Na+
/K+ ATPase

*Na+ /K+ -ATPase activity is stimulated by a rise in intracellular Na+ or extracellular K+

Question 16

The resting membrane potential of a neuron is primarily determined on the concentration gradient of which of the following ions?
Ca2+
Cl-
K+
Na+
A- (protein anions)

Answer 16

K+

The cell membrane is most permeable to K+. Diffusion of K+ out of the cell down the concentration gradient provides the driving force that sets up the membrane potential due to the separation of the positive charge carried by K+ efflux from the negative charge carried by the impermeable protein anions inside the cell. The contribution of other ions is small due to the lower membrane permeability to these ions.

Question 17

If the Na+/K+ ATPase is inhibited, the membrane potential of a nerve cell will slowly:
A. depolarize.
B. hyperpolarize.
C. depolarize and then hyperpolarize.
D. hyperpolarize and then depolarize.
E. approach the equilibrium potential of K+ ion.

Answer 17

A.

Suppose normal condition: cell becomes more negative as more + are pumped out = hyperpolarization
inhibiting the pump will cause the opposite: more posItive thus depolarize

Question 18

Which of the following is NOT required when calculating the resting membrane potential?
A. The absolute extracellular and intracellular concentrations of K+
B. The absolute extracellular and intracellular concentrations of Na+
C. The concentration ratio of Na+
D. The relative permeability to K+
E. The relative permeability to Na+

Answer 18

C

The concentration ratio of Na+ can only be used in the calculation of Na+ equilibrium potential. It cannot be used or substituted into the GHK equation for calculating the resting membrane potential.