Cardioselective sulfonylthiourea HMR 1098 blocks mitochondrial uncoupling induced by a K ATP channel opener, P-1075, in beating rat hearts

Abstract

We investigated effects of blockade of cardiac ATP-sensitive potassium channels (K ATP) with a novel cardioselective sulfonylthiourea, HMR 1098, on metabolic uncoupling caused by a potent K ATP opener, P-1075, in Langendorff-perfused rat hearts. We used (1) 87Rb-NMR to detect activation–deactivation of sarcolemmal K ATP, (2) 31P-NMR to monitor high-energy phosphates, (3) oxygen uptake measurements to monitor cellular respiration, and (4) myocardial optical absorbance measurements at 603 nm to follow changes in cytochrome c oxidase redox state. Activation of sarcolemmal K ATP by P-1075 (5 μM) and a mitochondrial uncoupler 2,4-dinitrophenol (DNP) (50 μM) stimulated Rb + efflux from the hearts by 130% and 60%, respectively. HMR 1098 (5 and 30 μM) blocked activation of sarcolemmal K ATP in situ. HMR 1098 also prevented cardiac arrest and mitochondrial uncoupling induced by P-1075, such as (a) depletion of phosphocreatine and ATP by 40%, (b) two-fold decrease in venous oxygen, and (c) reduction of cytochrome c oxidase (demonstrated by an increase in 603 nm optical absorbance). The metabolic effects of P-1075 can be readily explained by activation of putative mitochondrial K ATP. We concluded that blockade of mitochondrial uncoupling by HMR 1098 included an inhibiting effect of HMR 1098 on sarcolemmal and mitochondrial K ATP in beating rat hearts.