The role of the myocardial sodium-hydrogen exchanger in mediating ischemic and reperfusion injury. From amiloride to cariporide.

There is convincing evidence that the Na-H exchanger (NHE) plays a pivotal role in mediating tissue injury during ischemia and reperfusion. Extensive studies with NHE inhibitors have consistently shown protective effects against ischemic and reperfusion injury in a large variety of experimental models and animal species, particularly in terms of attenuating contractile dysfunction. These protective effects of NHE inhibition appear to be superior to other strategies, including ischemic preconditioning. Such studies have contributed greatly to the overwhelming evidence that NHE activation mediates ischemic and reperfusion injury. The NHE inhibitor HOE 642 (cariporide) is currently undergoing clinical evaluation in high-risk cardiac patients. Moreover, there is now emerging evidence that NHE may be involved in mediating cardiotoxicity directly produced by various ischemic metabolites such as lipid amphiphiles or reactive oxygen species. NHE inhibition also attenuates apoptosis in the ischemic myocardium, a process that may be of importance in the subsequent development of postinfarction heart failure. In conclusion, NHE represents an important adaptive process in response to intracellular acidosis that results in a paradoxical contribution to cardiac tissue injury.