Nitric Oxide Protects Cardiac Sarcolemmal Membrane Enzyme Function and Ion Active Transport against Ischemia-induced Inactivation

Nitric oxide (NO^.) generated from nitric oxide synthase (NOS) isoforms bound to cellular membranes may serve to modulate oxidative stresses in cardiac muscle and thereby regulate the function of key membrane-associated enzymes. Ischemia is known to inhibit the function of sarcolemmal enzymes, including the (Na⁺ + K⁺)-ATPase, but it is unknown whether concomitant injury to sarcolemma (SL)-associated NOS isoforms may contribute to this process by reducing the availability of locally generated NO^.. Here we report that nNOS, as well as eNOS (SL NOSs), are tightly associated with cardiac SL membranes in several different species. In isolated perfused rat hearts, global ischemia caused a time-dependent irreversible injury to cardiac SL NOSs and a disruption of SL NO^. generation. Pretreatment with low concentrations of the NO^. donor 1-hydroxy-2-oxo-3-(N-3-methyl-aminopropyl)-3-methyl-1-triazene (NOC-7) markedly protected both SL NOS and (Na⁺ + K⁺)-ATPase functions against ischemia-induced inactivation. Moreover, ischemia impaired SL Na ⁺/K⁺ binding, and NOC-7 significantly prevented ischemic injury to the ion binding sites on (Na⁺ + K⁺)-ATPase. These novel findings indicate that NO^. can protect cardiac SL NOSs and (Na⁺ + K⁺)-ATPase against ischemia-induced inactivation and suggest that locally generated NO^. may serve to regulate SL Na⁺/K⁺ ion active transport in the heart.