Membrane Biophysics HW

Membrane Biophysics HW

1. Shown below is a graph of an applied current Istim (nA) to a membrane and the measured membrane potential (mV). The conductances for Na, Cl, and Ca were zero. Thus one can study the K conductance. (a) How might these conductances been set to zero? (b) How else may one have isolated the K channels for study? (c) According to the graph, what is the Nernst potential for K? (show your work). (d) What is the measured K conductance? (show your work).

2)In class, and similar to what is shown above, we used Soma-conductances to get gK. Repeat this exercise in Soma 4 -conductances to get gNa. Open the lesson and set gK and gCl to 0. Leave gNa as is. You will likely need to use y-axis zoom out to get the whole graph of V vs Istim.Include a screen shot of the plot of V vs Istim (Use snip tool). Show you work.

3)Use Patch 2 K channel to calculate the conductance of the potassium channel like we did for Cl in class. Show you work and a screen shot.

4)Below is a measurement on a voltage clamped patch. The current (pA) is plotted vs time. (a) Why are there only two values of the current? (three if you count zero? (b) Why is the current sometimes zero? (c) What is the conductance of this channel? Assume that the concentration of K inside and outside are zero and notice that Vhold is +50 mV. (d) How would one determine if this channel is voltage gated? What would happen if it were or were not when you conduct the experiment you describe?

5)Below is a plot of an action potential. The membrane potential, and nernst potentials for Na and K (mV) as well as the total conductance (nS) are plotted against time. (a) What would happen if we lowered ENa? How would one accomplish lowering it? (b) What would happen if we raise EK? (c) What does this say about the nature of the action potential?

6)Using Axon_6 Dynamics. Explore the temperature dependence of the action potential. Change the temperature to 20 degrees and 6 degrees. Open parameter window by clicking P. Scroll down and change Temp. Include screen shots. What does temperature do?

7)Using Axon 8 impulse refractory, explore the cause of the refractory period. Basically repeat what we did in class for this, but pay attention to the conductances.

a)Hit 2x Pulse OFF box and open parameter modification window for 2x Pulse delay. Now 2x Pulse should be on and you will have two current stimulations that can be delayed w/r to each other.

b)Decrease time between pulses (echo delay), from 20 ms to 15 or 16 ms in steps of 1 ms. Show some screen shots. See that eventually no longer get second action potential. What is causing the refractory period?