CurrentClamp

Current clamp is a mode of electrophysiological recording and stimulation in which a controlled electrical current is injected into a cell and the resulting membrane potential is recorded. In typical experiments, an intracellular or extracellular electrode delivers a prescribed current through a low-noise amplifier, with the experimenter selecting the current amplitude and duration.

Because the current is prescribed and the membrane potential is free to respond, current clamp is well suited for studying neuronal excitability, action potential generation, and the input–output properties of cells. From the voltage trace, researchers determine the resting membrane potential, input resistance (from voltage deflections to current steps), and membrane time constant. By stepping current to various amplitudes, thresholds for action potential firing (rheobase) and firing patterns can be characterized.

Current clamp contrasts with voltage clamp, where the experimenter sets the membrane potential and measures the compensating current. In current clamp, the primary observable is membrane potential, whereas in voltage clamp the observable is current.

Related approaches include dynamic clamp, which uses real-time computation to inject synthetic conductances during a current-clamp experiment, and is often used to simulate ion channels or synaptic inputs.

In practice, current clamp is widely used in in vitro preparations such as brain slices and cultured neurons, and in computational models. In simulation environments like NEURON, the IClamp mechanism injects current into a segment of a modeled neuron to elicit responses.

Limitations include series resistance errors, electrode drift, and perturbations to the cell from intracellular recording; data interpretation must account for these factors.