Voltage Clamp

This section is largely composed of my notes on sections of Ionic CHannels of Excitable Membranes by Bertil Hille.
This is a technique developed by Marmont (1949), Cole (1949), and Hodgkin, Huxley, and Katz (1949, 1952)
The basic idea is that the voltage potential across a cell membrane is controled by the experimenter and the current is measured. Under these conditions the observed current can be a direct measure of ionic movements across the membrane to which the electrode is gripping.
In general, the current flow across the membrane is the sum of the ionic current and the capacitance current. The capacitance current is defined as i = C x (dv/dt). So, if the voltage level is quickly changed via a step function from one voltage to another, then the capcitance current is circumvented and we are left with a measure of the ionic current.
Currents carried by a particular ion should be inward if the voltage was set to a value negative relative to the equilibrium potential. Currents carried by a particular ion should be outward if the voltage was set to a value positive relative to the equilibrium potential. Finally, if the voltage is clamped to the equilibrium potential of a particular ion, then any current change would be due to the flow of other ions.

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    © 1995 Lance Hahn (lance@retina.anatomy.upenn.edu)