Actions of Nitric Oxide Synthase Inhibitors on Mitochondrial Respiration in Isolated Rat Heart Mitochondria

Abstract

ObjectiveThe existence of a nitric oxide (NO) producing enzyme, nitric oxide synthase (NOS), within cardiac mitochondria has been speculated in the most recent decades. There is conflicting data regarding the identity, physiological function, and the pathophysiological significance of mitochondrial NOS. Nevertheless, mitochondrial preparations have been shown to display an ability to produce NO that is sensitive to NOS inhibitors. Our objective was to evaluate the impact of pharmacological NOS inhibition on mitochondrial respiration. We hypothesized that pharmacological inhibition of NOS affects mitochondrial respiration.Methods and ResultsMitochondria were isolated from rats by homogenization and gradient separation. Isolated mitochondria were divided into three groups: untreated control, neuronal NOS inhibitor‐treated (nNOS; ARL dihydrochloride or ARL), and endothelial NOS inhibitor‐treated (eNOS; N5‐(1‐Iminoethyl)‐L‐ornithine or NIO). Mitochondrial function was assessed by measuring oxygen consumption rates (OCR) using Seahorse XFe Analyzer. First, we observed that isolated rat heart mitochondria displayed respiratory control ratios above 2 suggestive of the acceptable tightness of the coupling between respiration and phosphorylation indicative of the good quality of the preparation. Second, both NOS inhibitors decreased the OCR related to ATP production and increased proton leak in the mitochondria although the basal and maximal respiration were unaffected.ConclusionsPharmacological inhibition of NOS impairs ATP production in isolated rat heart mitochondria that is likely to be related to increased proton leak. Thus, the physiological function of mitochondrial NOS activity involves modulation of inner mitochondrial membrane permeability to promote efficiency of ATP productionSupport or Funding InformationAmerican Heart Association (PVG: 14SDG20490359 and VNS: 16PRE31450006); National Institute of Health: National Institute of Neurological Disorders and Stroke and National Institute of General Medical Sciences (PVK: R01NS094834); and National Institute of Diabetes and Digestive and Kidney Diseases (RS: DK107694).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.