MYOCARDIAL CATION-TRANSPORT

Background: Intracellular cations regulate a variety of functions in m yocytes, and abnormalities in ionic homeostatic control have been impl icated in several cardiac disease processes. These include cardiac hyp ertrophy, some of the cardiomyopathies and reperfusion injury followin g myocardial ischaemia. Topics under review: Current understanding of the sarcolemmal transport mechanisms which generate transmembrane elec trochemical gradients for Ca2+, H+ and K+ is reviewed. Both active, AT P-dependent membrane ion transport and secondary active transport are described. The importance of the sarcolemmal Na+-K+ pump in maintainin g transmembrane gradients for Na+ and K+ is emphasized, and we describ e how the electrochemical energy stored in the Na+ gradient generated by the pump is utilized by ion-exchange processes in which a tightly c oupled exchange of extracellular Na+ for intracellular Ca2+ or H+ occu rs. We also describe cotransport processes in which coupled obligatory transport of Na+, K+ and Cl- occurs in the same direction. Physiologi cal and pharmacological properties of sarcolemmal ion transport mechan isms are reviewed and reference is given to possible clinical implicat ions.