Increases in coronary collateral blood flow produced by sevoflurane are mediated by calcium-activated potassium (BK Ca) channels in vivo

Abstract

Background: Sevoflurane enhances coronary collateral blood flow independent of adenosine triphosphate-regulated potassium channels. The authors tested the hypothesis that this volatile anesthetic increases coronary collateral blood flow by either opening calcium-activated potassium channels or by directly stimulating nitric oxide synthesis in the canine coronary collateral circulation. Methods: Twelve weeks after left anterior descending coronary artery ameroid constrictor implantation, barbiturate-anesthetized dogs (n = 22) were instrumented for measurement of hemodynamics and retrograde coronary flow. Dogs received sevoflurane ([0.5 and 1.0 minimum alveolar concentration [MAC]) during intracoronary infusions of drug vehicle (0.9% saline), the calcium-activated potassium channel antagonist iberiotoxin (13 μg/min) or the nitric oxide synthase inhibitor Nω-nitro-L-arginine methyl ester (L-NAME, 300 μg/min). Retrograde coronary collateral blood flow was measured under baseline conditions, during and after administration of sevoflurane, and during intracoronary infusion of bradykinin. Data are mean ± SEM. Results: Sevoflurane increased (*P < 0.05) retrograde coronary collateral blood flow (from 65 ± 11 during control to 67 ± 12*and 71 ± 12*ml/min during 0.5 and 1.0 MAC, respectively). Iberiotoxin but not L-NAME attenuated these sevoflurane-induced increases in retrograde flow (6 ± 1*, 7 ± 2*, and 3 ± 2 ml/min during vehicle, L-NAME, and iberiotoxin, respectively). After discontinuation of sevoflurane, retrograde flow returned to baseline values in each group. Bradykinin increased retrograde flow in vehicle- (63 ± 12 to 69 ± 12*ml/min) but not in iberiotoxin- (61 ± 7 to 62 ± 5 ml/min) or L-NAME-treated dogs (64 ± 11 to 63 ± 10 ml/min). Conclusions: The results demonstrate that sevoflurane increases coronary collateral blood flow, in part, through activation of calcium-activated potassium channels in vivo. This action occurs independent of nitric oxide synthesis.