Biochemistry

Membrane Potential, Ion Channels and Goldman–Hodgkin–Katz Equation Problem with Answers

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The volume of compartment A = volume of compartment B = 1 liter. The compartments are separated by a membrane containing equal numbers of K+-only channels, Na+-only channels. When any of these channels are open, they allow movement of 1000 ions per nsec. At the start of the experiment, all channels are closed. The concentration of K+ is 140 mM on side A and 4 mM on side B; the concentration of (Na+) is 14 mM on side A and 150 mM on side B; the concentration of chloride ions (Cl-) is 154 mM on side A and 154 mM on side B. This system has no Na+/K+ATPase. The temperature is 37°C.

1. Experimental conditions are changed so that 50% of the K+ channels are opened. All Na+ channels remain closed. a. Calculate the membrane potential immediately after the channels are opened. b. Is the system at steady-state, or is it at equilibrium?

2. Ion concentrations returned to initial conditions, and 50% of the K+ channels and 10% of the Na+ channels are opened. a. Calculate the membrane potential immediately after the channels are opened b. The temperature is changed to 4° C. Calculate the membrane potential.

3. Ion concentrations are returned to initial conditions, and 50% of the Na+ channels and 10% of the K+ channels are opened. Calculate the membrane potential immediately after the channels are opened.