The regulation of mitochondrial NO synthase activity under nitroglycerine application in rat heart and liver mitochondria

Abstract

Nitroglycerine (NG) affords cardioprotection via NO formation, but the impact of NG application on reactive nitrogen species (RNS) metabolism remains little studied yet. Mitochondrial NO synthase (mtNOS) is an important endogenous source of RNS. Our aim was to study the effect of NG application on mtNOS activity and RNS production in rat heart and liver mitochondria. Different regulation of mtNOS activity in the heart and liver under NG treatment was found. While in heart mitochondria it increased dose-dependently, in liver mitochondria only moderate elevation and bell-shaped dose dependence of mtNOS activity on NG was observed. Nitrite and nitrate, which are the end products of L-arginine transformation by NOS, showed similar dose dependence on NG. To find an explanation for the observed dependences, we studied the effects of NG administration on the activity of arginase which competes with NOS for physiological substrate, Larginine. A strong reciprocal dependence between mtNOS and arginase activities was found. As we observed, the arginase activity increased under NG application. However, while in heart mitochondria high mtNOS activity agreed with moderate arginase activation, in liver mitochondria high arginase activity coincided with suppression of mtNOS activity at high doses of NG. Low arginase and high mtNOS activities observed in heart mitochondria were consistent with high NO2 − and NO3 − production and low hydroperoxide (H2O2) formation, whereas high arginase activity in liver mitochondria was accompanied by the reduction of NO2− /NO3− formation and simultaneous elevation of H2O2 production. A linear correlation between the arginase activity and hydroperoxide formation was found. We came to the conclusion that under NG administration arginase activation resulted in reciprocal regulation of RNS and ROS production in mitochondria, dependent on the proportion of mtNOS to arginase activity. Suppression of RNS metabolism could be the cause of ROS overproduction caused by high arginase and low mtNOS activity.