Abstract 18514: Rottlerin Greatly Improves Cardiac Functional Recovery Following Ischemic Cardioplegic Arrest (CP) in Wild-Type but Not BKCa Channel Knockout Mice

Abstract

Introduction: Mitochondrial BKCa channels are thought to provide protection during ischemic insults in the heart. Rottlerin, has been implicated as a potent BKCa activator, however this has not been firmly established. The purpose of this study was twofold: 1) investigate the efficacy of BKCa channel activation as a cardioprotective agent during cardioplegia/reperfusion (CP/R) and 2) assess the specificity of rottlerin for BKCa channels. Methods: Wt and BKCa KO mice were subjected to an isolated heart model of CP/R. Hearts were perfused for 30 min at 37C (baseline), followed by intermittent cold hypoxic CP with or without rottlerin (St Thomas II, 10C), and normoxic 37C reperfusion for 30 min. Mechanism of rottlerin-induced cardioprotection was also investigated using H9c2 cells subjected to in vitro CP/reoxygenation and assessed for mitochondrial membrane potential (TMRE) and ROS (DCFDA) production. Results: CP/R decreased LVDP (61.6 +/- 6 % baseline, n=6 ), +/- dP/dt (76.6+/- 7.3, 63.4 +/-7.7, % baseline respectively) and coronary flow (CF) (69.6+/-6.0 % baseline) in wt mice. Rottlerin, (100 nM (n=3), 500 nM (n=6)) dose dependently increased the recovery of LV function and CF to near baseline levels (% baseline 500 nM rottlerin, LVDP: 87.6+/- 4.0, +/-dPdt: 97.6 +/- 5.9, 90.9+/- 6.6, and CF: 125.3 +/-22.8, all p<.01 vs CP ). BKCa KO hearts treated with (n=7) or without (n=7) 500nM rottlerin, were similar to wt CP hearts (% baseline BKCa KO + 500 nM rott: LVDP: 66.9+/- 6.0, +/-dP/dt 73.0 +/-3.6, 65.2+/- 4.2, and CF: 94.1 +/- 9.0). H9c2 cells subjected to in vitro CP/R, displayed reduced mitochondrial membrane potential (39 +/-.09 % decrease) and increased ROS generation (50+/-.04% increase), both of which were significantly (p<.01) normalized by rottlerin (100 nM-1 uM) (n=8). Conclusions: Activation of BKCa channels profoundly rescues ischemic damage associated with CP/R, likely via effects on improved mitochondrial membrane potential and reduced ROS generation.