Question: Considering the net driving force and relative sodium conductance, exp
ID: 3476940 • Letter: Q
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Question: Considering the net driving force and relative sodium conductance, explain why INa first increases (When Vm is between -50mV to 0mV) and then decreases (when Vm is above +52mV), as shown in the graph of membrane current versus membrane potential. (Hint: you might find it helpful to calculate the net driving force and estimate the relative gNa at different membrane potentials.)
The data below were taken from a series of voltage clamp experiments. The data show the membrane current (bottom panel) that was measured in response to step depolarizations to 5 different command potentials (CP--26, 0, +26, +52 & +65mV; upper panel). Note there are two currents: an early, inward (black arrow) and a late, outward (blue arrow) currents, and that the capacitative and leakage currents have been removed S so 25 +52 2 4 68 Time (ms) For each command potential, the magnitude of the peak early (Na) current and the peak late (K') current were then plotted (figure, below left). Each command potential is noted with a red arrow These data illustrate the relation between command potential (membrane potential) and peak membrane current (i.e., the current flowing through open ion channels) for both the early and late currents of the action potential. The data on the right indicate the relation between membrane potential (command potential) and percentage of voltage-gated Na channels that open 3.0 Late 100% 2.0 0% 50 Command voltage (mV) RMP -100-50 Resting 50 Membrane potential (mV)Explanation / Answer
When Stimulus is given to resting membrane, change in potential leads to openng of voltage gated sodium channels resulting in influx of soium. But as the voltage is above +52mv the gradient decreases and also voltage gated channels are short lived. So inactivation of this voltage gated channels causes decreased conductance of sodium.
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