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Current Clamp

The current clamp method is used in electrophysiology to record the voltage of a cell membrane following an electric stimulus.

Not to be mistaken with the voltage clamp method, the current clamp method consists of an electrode that both records and injects current (flow of ions) inside a neuron. An additional electrometer outside the cell results in the recording of the resulting voltage. This technique could be used for example to mimic the electrical signal coming from a synapse and neurotransmitters, and observe their effect on the voltage of the axon membrane of a neuron.

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. Between 1 and 2.5 milliseconds, the voltage increases to -20 millivolts. Between 2.5 and 3 milliseconds, the voltage increases rapidly to 50 millivolts. Then between 3 and 5 milliseconds, there is an exponential decrease back to minus 70 millivolts. The voltage decreases below 0 millivolts at about 3.2 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 seconds the current is 0 nanoamps. At 1 millisecond the current increases to 0.33 nanoamps. The current stays at 0.33 nanoamps until 3 milliseconds, where the current drops back to 0 nanoamps. The current remains at 0 nanoamps for the next 2 milliseconds.

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

When the electrode does not inject current, the recorded voltage is the resting membrane potential, usually around -70 mV for neuronal membranes.

The current is usually injected in the form of short pulses, which are visualized as "square" signals on the recordings.

Referred from:

Article
Patch clamp technique