BSCI 426/Biol 622 Fall '14 Problem Set 10
assigned:
11/20/14
due:
12/02/14
1. The electrophysiological properties of a single channel were recorded in the presence of a salt gradient. Given that the reversal potential of the channel was -30 mV and the current at zero voltage was 20 pA,
a) what is its conductance?
b) what assumption did you have to make in order to estimate
the conductance?
2. This time the membrane contained two conductances. One of these was an ohmic conductance due to current traveling through pathways other than the channel being recorded (i.e. the "leak"). The other was current flowing through the channel. The reversal potential of the total current was -40 mV. When the channel closed, the reversal potential became -10 mV. When zero voltage was applied, the current varied from +6 pA to 0.5 pA as the channel gated between the open and closed state.
a) What are
the conductances of the channel and the "leak"?
b) What is the
reversal potential of the channel?
c) What are the
permeability ratios (Pcation/Panion)
for the channel and the "leak" using the constant field approximation
given the following conditions: The salt concentration on the ground side
(i.e. defined as 0 mV) was 10 mM KCl
while that on the side the voltage was measured was 100 mM
KCl. No other ions were present.