Role of ATP Sensitive Potassium Channel in Exercise-Training Mediated Adaptations in Ventricular Repolarization

Abstract

Regular exercise-training is known to reduce the incidences and severity of ischemic heart disease, but the mechanistic nature is unknown. We showed that regular exercise shortened the left ventricular action potential duration (APD) at high heart rate (HR), which would prevent Ca2+ overload and/or inadequate filling under conditions of metabolic stress. Here we test the hypothesis that exercise-training induced APD shortening at high HR is due to the up-regulation of ATP sensitive potassium channel (KATP). Female and male Sprague-Dawley rats were randomly assigned to voluntary wheel running or control groups. After 6-8 weeks training, cardiac myocytes were isolated from the apex and base regions of the left ventricle with collagenase–protease dispersion technique. APD was measured with glass micro-electrode, current-voltage relationship was recorded with discontinuous single electrode voltage clamp, and the expression level of KATP channel pore-forming subunit Kir6.2 and regulatory subunits SUR2A were determined by Western blots. At 1Hz, KATP activator pinacidil (100 µM) shortened APD in myocytes from both sexes and, the shortening was significantly greater in exercise-trained compared to sedentary groups. The KATP inhibitor glibenclamide (2 µM) prolonged the 10Hz APD more in exercise-trained than control rats. Regular exercise enhanced KATP outward current density in apex myocytes from both sexes; in base, trained females exhibited larger KATP inward current than controls. In both sexes, Kir6.2 expression was elevated by wheel-running in apex but not base region. Exercise-training increased SUR2A density in base region of both sexes, and eliminated its reginal difference in females. In conclusion, exercise-training induced APD shortening under energy demanding conditions (e.g. high HR) is caused at least in part by KATP up-regulation, an adaptation that reduces energy requirements for ion homeostasis and maintains a diastolic interval adequate for myocardial relaxation.