Channels and Transporters

Question 1

What did the voltage clamp experiments by Hodkin and Huxley predict?

Answer 1

separate Na+ and K+ channels
voltage sensors in channels
high conductance of channels to specific to specific ions

Question 2

What happens when patch clamp reaches +52 ? +65?

Answer 2

early inward sodium current missing; reverses to an outward current; as the cell becomes more positive the outward current of K+ channel inc. in magnitude

Question 3

Why is the patch clamp experiment important? Describe the mechanism of it.

Answer 3

allows for characterization of single channels (1st direct evidence)

glass pipette pressed against membrane-slight suction is applied to generate gigaseal
all current flows through the electrode and doesn’t leak
it tests microscopic current amplitude ~pA to several pA which is the current thru one channel

Question 4

Patch clamp recordings

Answer 4

detect current flowing thru single channel via depolarization

Question 5

What is gating?

Answer 5

transition between open and closed states; involves a temporary conformational change in the channel’s structure

Question 6

How are Na+ channels normally opened?

What does depolarization do to probability of channel opening? hyperpolarization?

Answer 6

random/stochastic opening of channels

deplorization increases changes, hyperoplarization decreases

Question 7

What comprises the macroscopic current in the patch clamp experiments?

Answer 7

aggregate of 1000s of microscopic currents which would represent single channels

Question 8

What is a key point of discovered by patch clamp experiments done on K+ channels?

Answer 8

k