Functional and cellular regulation of the myocardial Na+/H+ exchanger

The Na+/H+ exchanger is a pH-regulatory protein present in the plasma membr ane of cardiomyocytes and other cell types. In response to intracellular ac idosis, the protein removes one intracellular proton in exchange for an ext racellular sodium. The protein consists of a membrane transporting domain a nd a regulatory cytosolic domain. The regulatory cytosolic domain mediates the stimulation of the membrane domain. Hormonal stimulation of myocardial cells results in activation of the antiporter, possibly through protein kin ases and other regulatory proteins. Several hormones and growth factors hav e been shown to stimulate the antiporter in the myocardium, including endot helin, thrombin, angiotensin II, and alpha(1)-adrenergic stimulation. The e xact mechanisms involved in this stimulation are as yet unclear, and may be important in regulation of the Na+/H+ exchanger during ischemia and reperf usion.