Abstract 21186: Amelioration of Myocardial Stunning in Pigs Undergoing Cp/cpb With Bkca Channel Activator Supplemented Cardioplegia

Abstract

Introduction: Activation of mitochondrial large conductance Ca++-activated K+ channels (BKCa) is cardioprotective in cell and rodent isolated heart models of cardioplegic arrest and reperfusion. We previously demonstrated cardioprotection is associated with reduced mitochondrial ROS generation and reorganization of individual electron transport chain complexes into physically associated respiratory supercomplexes (SC) made of ETC complex I/III/IV. In this study, we examined the efficacy of BKCa activation during cardioplegic arrest in a clinically relevant large animal study using pigs subjected to CP/CPB and reperfusion. Methods: 50 kg Yorkshire pigs of either sex were subjected to CP/CPB (hyperkalemic cold blood CP, 1 hr) with or without the BKCa activator mallotoxin (MTX (aka rottlerin)) supplied in the CP solution, followed by reperfusion (1hr). Pigs were instrumented with a PV catheter and IVC occlusions performed at baseline and 30 and 60 mins after weening from bypass. Following surgery, mitochondria were isolated and subjected to Blue-Native PAGE and immunoblotting of ETC complexes to visualize large (~100-1500 kD) mitochondrial SC. Results: Baseline hemodynamics were similar between groups. CP/CPB resulted in significant myocardial stunning in pigs as assessed by LVDP (pre 64.8 mmHg vs post 42.0, P<.05 ), +/-dP/dt (pre 971.4 and -911.8 vs post:588.0 and -541.0, P<.05 ), and end-systolic elastance (Ees: pre 1.28 vs post .63, P=0.1 ) at 60 min reperfusion. However, pigs arrested with CP containing MTX (500 nM) exhibited greatly reduced myocardial stunning with significant improvements in LVDP (pre:65.7 post:67.8 mmHg, P<.01 vs post CP/CPB group) +/- dP/dt (pre:1026.0 and -911.8 vs post:1441.7 and -984.8 mmHg/s, P=.02 and .04 vs CP/CPB) and Ees (pre 1.1, post 1.35, P=.02 vs CP/CPB). LV mitochondria isolated from both groups had two major I/III/IV mitochondrial SC’s of ~1300 (SC1) and ~1000 kD (SC2) as assessed by BN-PAGE and immunoblot. The CP/CPB + MTX group had significant increases in both SC1 (6.0 % vs 18.0%, P=.01) and SC2 (19.7% vs 52.3%, P<.01) expressed as percent of total assembled complex IV. Conclusion: Addition of a BKCa activator to CP solutions ameliorates myocardial stunning in large animals subjected to CP/CPB and reperfusion.