Voltage clamp

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  1. Technique for setting the transmembrane potential at a chosen value; the voltage clamp circuit holds the membrane potential at this level and then measures the net ionic current that flows across the membrane during the clamp
    1. in an environment where the intra and extracellular concentration of Na is the same, if the transmembrane potential is clamped to 0 there is no net force causing Na to flow and no electrical potential difference; when this is done the inward current disappears indicating that Na is the cause of the inward current; this isolates the K current
    2. if the transmembrane potential is clamped at +58 mV, the Na equilibrium potential, no net Na flow occurs and the inward current disappears; clamping at >58 mV causes an outward Na current
    3. this experiment was able to show that the three parts to an action potential were the increase in Na conductance, the return of Na conductance to resting levels and the increase in K conductance
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