Electrophysiology III: The Hodgkin-Huxley Model

Question 1

How do you calculate driving force?

Answer 1

Vm (membrane potential) - E ion (Ion equilibrium potential)

Question 2

What is the ionic permeability hypothesis?

Answer 2

The permeability changes of an ion during AP consists of a rapid but transient increase in permeability to Na+ and a delayed increased in the permeability to K+. It is suggested that both permeability changes vary with membrane potential in a graded but reversible manner due to gated channels.

Question 3

How can you show experimentally that Vm depends on Ek?

Answer 3

• Change extracellular K+ systematically
• if [K+]e > [K+]i, then Vm is ??

Question 4

How do you test the ionic permeability hypothesis?

Answer 4

• Ionic current = conductance x driving force
• IK = gK (Vm - EK)
• INa = gNa (Vm - ENa)

need to measure g(ion) to show V dependence then work out I(ion) for any Vm change

Question 5

What is the ideology on the voltage clamps?

Answer 5

Reasoned that if Vm could be held (clamped) at any desired test voltage, then I ion could be measured, and hence g ion determined for voltage