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Voltage clamp

Voltage clamp method is used in electrophysiology to record the ion current through the membranes of excitable cells, such as neurons while maintaining a fixed membrane voltage. As opposed to current clamp method, the voltage clamp method controls the membrane potential.

How does voltage clamp method work?

A basic voltage clamp will iteratively measure the membrane potential using two electrodes, and then change the membrane potential (voltage) to the desired fixed value by adding the exact necessary amount of current through injection of ions. This "clamps" the cell membrane at a desired constant voltage while also recording what currents are being delivered to achieve the constant voltage. Because the currents applied to the cell must be equal to (and opposite in charge to) the current going across the cell membrane at the set voltage, the recorded currents indicate how the cell, or a specific ion channel, reacts to changes in membrane potential. It is important to use the appropriate buffer when studying specific ion channels in patch clamp studies.

There are 2 graphs. In the first graph, the voltage in millivolts is on the y axis, and the time in milliseconds is on the x axis. At 0 milliseconds the voltage is minus 70 millivolts. At 1 millisecond the voltage rises to minus 5 millivolts. The voltage remains at minus 5 millivolts for the next 4 milliseconds. In the second graph, the current in nanoamps is on the y axis, and the time in milliseconds is on the x axis. At 0 milliseconds the current is 0 nanoamps. At 1 millisecond the current decreases to minus 3 nanoamps. Then the current increases to 0 nanoamps between 1 and 3 milliseconds. This increase is initially steep between 1 and 2 milliseconds, before becoming a more gradual increase after 2 milliseconds, e.g. an exponential. The current remains at 0 nanoamps for the next 2 milliseconds.

Figure 1: Example of current recording with the voltage clamp method

Referred from:

Article
The Hodgkin and Huxley Model