[Potassium and magnesium in the myocardial cell: general data].

The aim of this introductory paper is to describe the movements of the two major cations of the myocardial intracellular compartment, potassium and magnesium. The role of the potassium ion, which participates in an active manner in the development of transmembrane potential changes during the cardiac cycle, is treated in terms of membrane conductance, driving force and active transport (Na-K-ATPase). The magnesium ion, of which role mainly concerns intracellular metabolic activity and interactions on the membrane exchanges of other ions is considered under three main aspects: its action on Na-K-ATPase and its effects on the electrophysiological properties and contractile activity of the cardiac fibres. Disturbances of the exchanges of these two cations during myocardial ischaemia and their importance in the field of cardioplegia are briefly discussed.