Cardiac cellular electrophysiology: past and present

Summary The time-course of the cardiac action potential can be accounted for in terms of ionic currents crossing the cell membranes. Depolarizing current is carried by Na⁺ or Ca²⁺ entering the cells, repolarizing current by K⁺ leaving the cells. Membrane permeability for the passive movement of these ions is thought to be voltage-dependent as well as time-dependent. Net transfer of charge may also result from active transport, 2 Na⁺ out against 1 K⁺ in; or coupled exchange, 3 or 4 Na⁺ in against 1 Ca²⁺ out. This review follows the path by which present-day knowledge has been reached. It also gives a few examples to illustrate that electrophysiology has provided concepts useful to clinical cardiology.