Possible role of sarcolemmal Ca2+/Mg2+ ATPase in heart function.

The Ca2+/Mg2+ ATPase, which is activated by millimolar concentrations of Ca2+ or Mg2+, has been found to exist in the heart sarcolemmal membrane. Although a great deal of work has been carried out to characterize the enzyme activity as well as to purify the enzyme, the physiological function of the enzyme remains to be elucidated. This enzyme has been shown to be different from other known ion transport ATPases such as Na(+)-K+ ATPase and Ca2(+)-stimulated ATPase in terms of the activation kinetics of various cations, the sensitivity towards specific inhibitors, and the molecular weights. In view of the existing data and circumstantial evidence, it has been proposed that the Ca2+/Mg2+ ATPase is involved in the entry of Ca2+ into the cardiac cells, the transport of Mg2+ across the cell membrane, and extracellular ATP signal transduction.