Myocardial cation transport

BACKGROUND: Intracellular cations regulate a variety of functions in myocytes, and abnormalities in ionic homeostatic control have been implicated in several cardiac disease processes. These include cardiac hypertrophy, some of the cardiomyopathies and reperfusion injury following myocardial ischaemia. TOPICS UNDER REVIEW: Current understanding of the sarcolemmal transport mechanisms which generate transmembrane electrochemical gradients for Ca2+, H+ and K+ is reviewed. Both active, ATP-dependent membrane ion transport and secondary active transport are described. The importance of the sarcolemmal Na(+)-K+ pump in maintaining transmembrane gradients for Na+ and K+ is emphasized, and we describe how the electrochemical energy stored in the Na+ gradient generated by the pump is utilized by ion-exchange processes in which a tightly coupled exchange of extracellular Na+ for intracellular Ca2+ or H+ occurs. We also describe cotransport processes in which coupled obligatory transport of Na+, K+ and Cl- occurs in the same direction. Physiological and pharmacological properties of sarcolemmal ion transport mechanisms are reviewed and reference is given to possible clinical implications.