The role of sodium-proton exchange in ischemic/reperfusion injury in the heart. Na(+)-H+ exchange and ischemic heart disease.

Previous work has associated cardiac dysfunction and damage after ischemia/reperfusion with metabolic alterations in the heart or alterations in the myocardial ionic homeostasis. Unfortunately, neither mechanism on its own has been able to conclusively explain the pathology. Instead, recent data suggest that the two mechanisms may be interrelated. The low intracellular pH during ischemia (due to the accumulation of metabolic by-products) may stimulate the Na(+)-H+ exchange pathway during reperfusion to remove H+ from the cell in exchange for will lead to accelerated Ca2+ entry via Na+. The subsequent accumulation of Na+ in the cell Na(+)-Ca2+ exchange, which can ultimately result in intracellular Ca2+ overload, contractile dysfunction and damage. This hypothesis is supported by the known biochemical characteristics of the cardiac Na(+)-H+ exchanger. Pharmacological studies also support this hypothesis as a mechanism involved in ischemic/reperfusion damage. Dimethylamiloride, a blocker of Na(+)-H+ exchange, has provided significant protection against ischemic/reperfusion injury to the heart. A series of studies have indicated that the mechanism through which dimethylamiloride acts is via inhibition of the Na(+)-H+ exchange pathway. The data, therefore, are consistent with an important interaction between metabolism and ionic alterations, which includes a central role for Na(+)-H+ exchange in ischemic/reperfusion damage to the heart.