Lecture0927final

Lecture0927final - Box A Voltage Clamp Method 3.1 Current...

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Box A Voltage Clamp Method

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3.1 Current flow across an axon membrane during a voltage clamp experiment. Depolarization elicits a large transient inward followed by a large delayed outward current
What happens to the membrane current s when different steps of voltage are commanded to different levels of V m ?

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3.3 Relationship between current amplitude and membrane potential. Late = K current Early = Na current
V m Outside cell Inside cell i leak i Na (“-ve”; i.e. into cell) i k For V m < -50 mV the votage-dependent Na and K channels open, g Na and g K increase and currents flow through them

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Interpretation of V-I curves in terms of the electrical model 1) Both i Na and i K are activated when the membrane is depolarized. 2) The early current is i Na i Na = g Na (V m -E Na ) – so the early current reverses from inward (negative) to outward (positive) when Vm exceeds E Na = +58 mV. 3) The late current is I K i K = g K (V m -E k ) – so the late current is outward (positive) at all membrane potentials more positive than E k = -70mV. 4) The term V m -E ion represents a DRIVING FORCE that drives an ionic
V m Outside cell Inside cell i leak i Na (“-ve”; i.e. into cell) i k

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3.4 Proof that the early inward current is due to sodium – the early current reverses to flow outward if [Na+] out is reduced so it becomes LESS than [Na+] out .

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This document was uploaded on 10/27/2011 for the course BSCI 453 at Maryland.

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Lecture0927final - Box A Voltage Clamp Method 3.1 Current...

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