INTRODUCTION TO CATION REGULATION IN THE MYOCARDIUM

Publisher Summary This chapter discusses the various aspects of cation regulation in the myocardium. Intracellular Na + and H + ion activities measured with ion-sensitive microelectrodes have profound effects on cardiac function such as cell-to-cell spread of excitation. A major route through which K + ions pass through the plasma membrane is a set of ion channels that exhibit inward going rectification. A finely balanced ionic milieu in the cardiac cell is essential for the proper function of the heart. The major inorganic cations, namely, K + , Na + , Ca 2+ , and Mg 2+ , are not only unequally distributed between extracellular space and cell interior but also within the cell. In recent years, it has become apparent that cell organelles such as sarcoplasmic reticulum, mitochondria, or nuclei may contain an ionic composition quite different from that of the cytosol. While the distribution of Na + and K + ions across the cell membrane profoundly affects excitability of the membrane, small variations of the distribution of Ca 2+ ions within the cell have considerable effects on the conformation of contractile proteins and regulate contractility of the heart.