Current clamp prescribes injected electric current while recording membrane potential. A constant command does not force membrane potential to remain constant: a neuron can produce action potentials or synaptic potentials while that command is unchanged. At zero commanded electric current, the amplifier still measures membrane potential; intrinsic ionic electric currents continue. The name concerns current supplied by the instrument, not the cancellation of all currents in the biological cell.
In whole-cell recording, the measured pipette voltage during a current pulse includes the patch-clamp series resistance drop. A modern authored methods article explicitly describes current-pulse protocols and this distortion.[ref]
Multiple Two-Photon Targeted Whole-Cell Patch-Clamp Recordings From Monosynaptically Connected Neurons in vivo by Jean-Sébastien Jouhanneau and others. Intracellular Current Injection; Step 5: Whole-Cell Configuration
Check the access contribution with small pulses and distinguish the immediate pipette-voltage jump from the slower membrane capacitance response. A zero-input interval measures a baseline, not proof that the instrument has no voltage offset. The passive example below explains these distinctions without asserting any new physiological measurements. New to topics? Read the docs here!