Question

Question 4 (3 pts) You are patch-clamping a cell. While holding the neuron at different membrane potentials, you observed the current recordings below.

(1 pt) How many channels does your patch likely contain?

(2 pt) Given the recordings above, what is the reversal potential for the channel? Explain your reasoning in 1 sentence.

b.(2 pt) Is there any net flow of ions at the resting potential in part ‘b’ above? Why or why not?

c.(2 pt) You discover that there are also K+ ions present at the same intracellular and extracellular concentrations as the Mg+2 ions (although there are no channels for the K+ ions to pass through). What is the Nernst potential of K+? Explain your thinking.

d.(1 pt) Assume that the resting potential of the neuron is -40 mV. You are conducting a voltage clamp experiment, and decide to depolarize the membrane by 25 mV. What is the new membrane potential?

Answer 1

a)

In 5 mV, one ion channel undergo transition between open and close form. In -10 mV, no ion channel undergo transition. In -50 mV, another one ion channel undergo open and close transitions. So 2 channels are likely to be there.

At reversal potential, the ion channels do not undergo transition between open and close form. In this case, the reversal potential is -10 mV.

b) Ions flow through the membrane when they are open. In case of -10mV (part 'b' above), there are no channels that are open for the ions to flow.

ANSWER: No. there is no net flow of ions at the resting potential in part ‘b’ above.