EFFECTS OF NICORANDIL ON ELECTRON TRANSPORT CHAIN ACTIVITY IN SKELETAL MUSCLE MITOCHONDRIA

Abstract

In skeletal muscle, pharmacological modulation of the mitochondrial ATP‐sensitive K+ channel (mitoKATP) represents an strategy in myoprotection against metabolic stress. The role of mitoKATP channel in different tissues has been proposed by its participation in several signaling routes that promotes the production of ATP, affecting the transfer of energy between mitochondria and cellular ATPases. However, it has been reported that the action of activators of mitoKATP channels besides acting on the channels, could also have effects on different structures at mitochondrial level. Nicorandil has been recognized as a selective mitoKATP channel opener, making it a useful tool for determining the importance of this mitochondrial site. It is considered an effective drug for the treatment against ischemia‐reperfusion injury and fatigue in skeletal muscle, however its effects on mitochondrial respiration remains unclear. Hence, the aim of this study was to explore the effects of nicorandil on the activity of the electron transport chain (ETC) in isolated mitochondria derived from chicken skeletal muscle.Mitochondria from pectoralis muscle of 2‐week‐old Arbor Acres chickens were isolated by differential centrifugation. The rate of oxygen consumption was determined at room temperature using a Clark‐type oxygen electrode coupled to an oxygen monitor YSI 5300 and a computer for data acquisition. The determinations started after adding 10 mM glutamate/malate as respiratory substrate for complex I (state 4) and 1 mM ADP was added to determine oxygen consumption in the phosphorylating state (state 3). The activities of the ETC complexes were (I–IV) were assayed spectrophotometrically in a Perkin Elmer Lambda 18UV/vis spectrophotometer using 0.5 mg/mL mitochondria resuspended in 50 mM KH2PO4buffer. NADH‐oxidoreductase (complex I) activity was evaluated by measuring the oxidation of NADH at an absorbance of 340 nm; Succinate‐DCIP oxidoreductase (complex II) activity was measured at 600 nm by following the reduction of 2,6‐dichlorophenolindophenol (DCIP). Antimycin A‐sensitive succinate‐cytochrome oxidoreductase (complex III) activity was followed by measuring at 550 nm the reduction of cytochrome. Cytochrome oxidase (complex IV) activity was evaluated by measuring the oxidation of reduced cytochrome at 550 nm.Nicorandil (10 μM) significantly decreased respiration (31.59 ± 6.15 %.) compared with control condition; this effect on oxygen consumption in the respiratory state 3 is associated with changes in the enzymatic activity of complexes II, III and IV. These findings suggest and question the assumption that sensitivity to nicorandil implies involvement of mitoKATP channels. Therefore, we suggest that effects pharmacological by nicorandil may be related to its effects on respiratory chain complexes.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.