Rottlerin Increases Cardiac Contractile Performance and Coronary Perfusion Through BK _Ca++ Channel Activation After Cold Cardioplegic Arrest in Isolated Hearts

Abstract

Background Cardioplegia and cardiopulmonary bypass(CP/CPB) subjects myocardium to complex injurious stimuli that can result in cardiomyocyte and vascular contractile abnormalities. Rottlerin, originally identified as a PKCδ inhibitor has a number of known additional effects that may be beneficial in the setting of CP/CPB. We tested the hypothesis that rottlerin would mitigate deleterious effects associated with CP/CPB. Methods and Results Langendorff-perfused isolated rat hearts were subjected to 2 hours intermittent cold (10 deg C) cardioplegia (St Thomas II) followed by 30 min normothermic reperfusion. Cardioplegia was delivered every 30 min, for 1 min. Hearts were treated with (CP+R, n=7) or without (CP, n=9) the PKCδ inhibitor, rottlerin (1μM) and/or the BKCa++ channel inhibitor Paxilline (100 nM) supplied in the cardioplegia. Hearts constantly perfused with Krebs-Heinslet buffer served as controls (n=6). Baseline parameters of cardiac function were similar between groups. CP resulted in reduced cardiac function (LVDP:39±3.8%,±dP/dt: 32±4.4%,-41±5.1% decrease compared to baseline). Treatment with 1uM Rottlerin significantly improved CP-induced cardiac function (LVDP: 20±5.9%, ±dP/dt: 5.2 ±4.5%, -11.6 ± 4.7% decrease versus baseline, (p < .05 CP+R vs CP)). Rottlerin also caused a significant increase in coronary flow post reperfusion (CP 34±4.2% decrease from baseline, vs CP+R 26±9.6% increase over baseline, p=.01). Independent of vascular effects, CP significantly decreased isolated myocyte contraction which was restored by rottlerin treatment. The BKCa++ channel inhibitor greatly reduced the majority of beneficial effects associated with Rottlerin. Conclusions Rottlerin significantly improves cardiac performance following cardioplegic arrest via improved cardiomyocyte contraction and coronary perfusion.

Ca²⁺-Activated K⁺ Channels as Therapeutic Targets for Myocardial and Vascular Protection

“…BKCa activation with rottlerin significantly improved LVDP and dP/dt, as well as promoted enhanced coronary flow. 36 We have also confirmed specificity of rottlerin's effects using wildtype and BKCa KO mice, as well as verified significant cardioprotection with rottlerin-supplemented cardioplegia in a pig model of cardioplegia and cardiopulmonary bypass 37 (unpublished observations). Myocardial stunning associated with mild ischemic insults is an additional sion pattern SK1>SK2>SK3.…”

“…55 Indeed, BKCa activation during hypothermic IR significantly increases coronary flow, which is associated with improved function. 36 In addition, precipitating conditions of ischemic heart disease (hypercholesterolemia, diabetes, and metabolic syndrome) are all associated with impaired vasodilation and altered vasoreactivity. A large body of work (outside the scope of the current review) demonstrates that vascular perturbations in these diseases are all associated with altered expression, activity, and upstream signaling associated with BKCa channel subunits (for review 2,56 ).…”

BKCa channel activation increases cardiac contractile recovery following hypothermic ischemia/reperfusion

“…We recently demonstrated that the small molecule rottlerin (mallotoxin) enhances cardioprotection following ischemic cardioplegic arrest and reperfusion (CP/R) in a rat model of mild ischemic injury and myocardial stunning (10). Early evidence indicated that the cardioprotective effect of rottlerin was mediated by BKCa channels as demonstrated by pharmacological inhibition of the channel with paxilline.…”

“…Isolated heart model of CP/R was performed similar to previous publications (10,11). FVB WT and kcnma1…”

“…Mouse myocytes were isolated similarly to previously published rat protocols (10,11). Mouse hearts were rapidly excised as detailed above, and Langendorff was perfused with perfusion media (MEM) (GIBCO, Carlsbad, CA) (Joklik modification supplemented with 20 M CaCl2, creatine, taurine, and carnitine) for 5 min.…”