Arterial Smooth Muscle BK Channel Beta1 Subunits Determine Ethanol-Induced Cerebrovascular Constriction

Abstract

Ethanol at concentrations obtained in circulation after binge drinking (≤50 mM) causes cerebrovascular constriction, which primarily results from ethanol-induced inhibition of arterial smooth muscle voltage- and calcium-gated potassium (BK) channels (Liu et al., 2004). Cerebrovascular myocyte BK channels are made of channel-forming α (encoded by KCNMA1) and smooth muscle-abundant β1 subunits (encoded by KCNMB1). After cloning α (“cbv1”, AY330293) and β1 (FJ154955) subunits from rat cerebral artery myocytes, we set to identify the molecular effector of ethanol-induced inhibition of channel activity and cerebrovascular constriction. Cbv1 and cbv1+β1 channels were expressed in Xenopus oocytes and channel steady-state activity (NPo) was recorded in inside-out (I/O) macropatches at a wide Ca2+i range (0.3-100 μM). Ethanol potentiated current at Ca2+i 30 μM. Beta1 subunits shifted the crossover for ethanol-induced macroscopic current potentiation to inhibition towards lower Ca2+i (≤3 μM). This shift was paralleled by a similar shift in NPo. To evaluate β1-modulation of ethanol action in native channels, we probed ethanol on BK channels in cerebral artery myocytes isolated from wt (C57BL/6) and KCNMB1 K/O mice. Recordings were performed in I/O patches, at Vm=-20, -40mV and Ca2+i=10 μM. In myocytes from wt mice (having BK made of α and β1 subunits) 50 mM ethanol significantly decreased NPo (-23.4±9%). In contrast, ethanol reversibly increased NPo in KCNMB1 K/O myocytes. Finally, we pressurized isolated mouse cerebral arteries and evaluated the impact of β1 subunit modulation of ethanol action on organ function. In vessels from wt animals ethanol caused a robust decrease in diameter (-14%). In contrast, KCNMB1 K/O vessels were resistant to this ethanol action. Our data indicate that BK β1 subunits are the functional targets mediating ethanol-induced cerebrovascular constriction. NIH Grant AA11560 (AMD).