Use the following constants: Gas constant R: 1.987 cal K-1 mol1 Faraday constant

Question

Use the following constants: Gas constant R: 1.987 cal K-1 mol1 Faraday constant F: 23,000 cal V1 mol g the Nernst equation, calculate the equilibrium potential for K' under following conditions. [K'ln 105mM; [K'lout 5mM; Temperature: 31°C 1. Usin 2. A: Usin g the Goldman equation, calculate the membrane potential Vm for out- out 140mM; [Cln: 10mM; Cout: 120mM; Temperature: 21°C; for relative permeabilities assume that pk. pNa-po-1 : 0.04: 0.45 B: Calculate how Vm would change if p PNa: 1:20: 0.40 (show math!) C: Under which conditions would you expect to measure values calculated in (A) and (B)? 3. A neuron is whole cell voltage-clamped from its resting membrane potential of -70mV to -35mV. The threshold for firing an action potential in this cell is -45mV after the clamping step. time showing the neuron's response to the change in membrane voltage A: Draw a voltage trace over time reflecting the voltage before and B: Using the same time line as in (A), draw a current trace over drawn in (A) C: Using the same time line as in (A), draw a current trace over time showing the neuron's response to the change in membrane voltage drawn in (A) in the presence of a blocker of voltage-gated Na channels. D: Using the same time line as in (A), draw a current trace over time showing the neuron's response to the change in membrane voltage drawn in (A) in the presence of a blocker of voltage-gated K' channels.

Explanation / Answer

Q.1

Solution:

Formula: EK = [ RT / ZF ] * ln { [K+]out / [K+]in }

Given:

R = 1.987 cal. K-1. mol-1,

T = 304.15 K,

Z = 23,000 cal . V-1. mol-1,

[K+]out = 5mM,

[K+]in = 105mM

Substitute the given value in the equation,

EK = (1.987 * 304.15 / 1 * 23,000) * ln (5/105)

     = 0.02627 * -3.0445

     = -0.079979015 V

The value is in V, we have to convert it to mV: For mV conversion multiply the answer with 1000.

-0.079979015 * 1000 = 79.97mV

Answer: 79.97mV

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