Bepridil, an Antiarrhythmic Drug, Opens Mitochondrial KATPChannels, Blocks Sarcolemmal KATPChannels, and Confers Cardioprotection

Abstract

Bepridil, which is clinically useful in the treatment of arrhythmias, has been reported to inhibit sarcolemmal ATP-sensitive K⁺ (sarcK_ATP) channels. However, the effect of bepridil on mitochondrial ATP-sensitive K⁺ (mitoK_ATP) channels remains unclear. The objective of the present study was to determine whether bepridil activates mitoK_ATP channels and confers cardioprotection. SarcK_ATP channels composed of Kir6.2+SUR2A in human embryonic kidney (HEK) 293 cells were examined using the patch-clamp technique. Flavoprotein fluorescence in guinea pig ventricular cells and matrix volume in isolated rat heart mitochondria were measured to assay mitoK_ATP channel activity. Mitochondrial Ca²⁺ concentration ([Ca²⁺]_m) was measured by loading cells with rhod-2 fluorescence. Coronary-perfused guinea pig ventricular muscles were subjected to 35-min no-flow ischemia followed by 60-min reperfusion. Bepridil (10 μM) completely inhibited the pinacidil-induced Kir6.2+SUR2A channel current expressed in HEK 293 cells. Bepridil reversibly oxidized the flavoprotein and increased mitochondrial matrix volume in a concentration-dependent manner. Furthermore, bepridil significantly attenuated the ouabain-induced increase of [Ca²⁺]_m. Pretreatment with bepridil for 5 min before ischemia improved the recovery of developed tension measured after 60 min of reperfusion. These effects of bepridil were abolished by the mitoK_ATP channel blocker 5-hydroxydecanoate (500 μM) and by the nonselective K_ATP channel blocker glisoxepide (10 μM). Our results indicate that bepridil is an opener of mitoK_ATP channels but an inhibitor of sarcK_ATP channels and exerts a direct cardioprotective effect on native cardiac myocytes. This is the first report of a unique modulator of K_ATP channels; bepridil would be expected to mitigate ischemic injury while blunting arrhythmias.