Module 7.2 - Single channel currents of KV and NaV channels

Question 1

What were H&H recording in the squid axon?

Answer 1

Macroscopic currents

Question 2

What are macroscopic currents?

Answer 2

sum single channel currents of all NaV and KV channels present in a recorded neuron or axon

Question 3

Who invented the patch clamp technique?

Answer 3

Erwin Neher and Bert Sakmann

Question 4

What is the significance of the patch clamp technique?

Answer 4

Permits recording of single ion channel currents

Question 5

What did H&H note in their voltage clamp experiments? (3)

Answer 5

1. At first, depolarization caused an increase in peak macroscopic INa amplitude
2. But with even stronger depolarization, peak INa maxed out and began to decline
3. Eventually, peak INa reached 0 and reversed

Question 6

Explain the reasons for the three INa trends H&H noted.

Answer 6

1. At first, Na+ currents got bigger because increased depolarization activated more and more NaV channels and thus increased GNa
2. But each voltage step incrementally decreased the DF for the Na+ currents
3. Once all channels have been activated, maxing GNa out to a constant, peak current will shrink and then reverse as Vm approaches and surpasses ENa

Question 7

What happens to GK and DF for the K+ currents at each depolarizing step? Why?

Answer 7

GK and DF both increase.
Increased depolarization activates more and more KV channels (increases GK) while moving Vm further from EK (increasing DF)

Question 8

What prize did Neher and Sakmann receive for their invention of the patch clamp technique?

Answer 8

1991 Nobel Prize in Physiology or Medicine