Effects of KATP channel openers diazoxide and pinacidil in coronary-perfused atria and ventricles from failing and non-failing human hearts

Abstract

This study compared the effects of ATP-regulated potassium channel (KATP) openers, diazoxide and pinacidil, on diseased and normal human atria and ventricles. We optically mapped the endocardium of coronary-perfused right (n=11) or left (n=2) posterior atrial–ventricular free wall preparations from human hearts with congestive heart failure (CHF, n=8) and non-failing human hearts without (NF, n=3) or with (INF, n=2) infarction. We also analyzed the mRNA expression of the KATP targets Kir6.1, Kir6.2, SUR1, and SUR2 in the left atria and ventricles of NF (n=8) and CHF (n=4) hearts. In both CHF and INF hearts, diazoxide significantly decreased action potential durations (APDs) in atria (by −21±3% and −27±13%, p<0.01) and ventricles (by −28±7% and −28±4%, p<0.01). Diazoxide did not change APD (0±5%) in NF atria. Pinacidil significantly decreased APDs in both atria (−46 to −80%, p<0.01) and ventricles (−65 to −93%, p<0.01) in all hearts studied. The effect of pinacidil on APD was significantly higher than that of diazoxide in both atria and ventricles of all groups (p<0.05). During pinacidil perfusion, burst pacing induced flutter/fibrillation in all atrial and ventricular preparations with dominant frequencies of 14.4±6.1Hz and 17.5±5.1Hz, respectively. Glibenclamide (10μM) terminated these arrhythmias and restored APDs to control values. Relative mRNA expression levels of KATP targets were correlated to functional observations. Remodeling in response to CHF and/or previous infarct potentiated diazoxide-induced APD shortening. The activation of atrial and ventricular KATP channels enhances arrhythmogenicity, suggesting that such activation may contribute to reentrant arrhythmias in ischemic hearts.