Essential role for smooth muscle BK channels in alcohol-induced cerebrovascular constriction

Abstract

Binge drinking is associated with increased risk for cerebrovascular spasm and stroke. Acute exposure to ethanol at concentrations obtained during binge drinking constricts cerebral arteries in several species, including humans, but the mechanisms underlying this action are largely unknown. In a rodent model, we used fluorescence microscopy, patch-clamp electrophysiology, and pharmacological studies in intact cerebral arteries to pinpoint the molecular effectors of ethanol cerebrovascular constriction. Clinically relevant concentrations of ethanol elevated wall intracellular Ca 2؉ concentration and caused a reversible constriction of cerebral arteries (EC50 ‫؍‬ 27 mM; Emax ‫؍‬ 100 mM) that depended on voltage-gated Ca 2؉ entry into myocytes. However, ethanol did not directly increase voltage-dependent Ca 2؉ currents in isolated myocytes. Constriction occurred because of an ethanol reduction in the frequency (؊53%) and amplitude (؊32%) of transient Ca 2؉ -activated K ؉ (BK) currents. Ethanol inhibition of BK transients was caused by a reduction in Ca 2؉ spark frequency (؊49%), a subsarcolemmal Ca 2؉ signal that evokes the BK transients, and a direct inhibition of BK channel steady-state activity (؊44%). In contrast, ethanol failed to modify Ca 2؉ waves, a major vasoconstrictor mechanism. Selective block of BK channels largely prevented ethanol constriction in pressurized arteries. This study pinpoints the Ca 2؉ spark͞BK channel negative-feedback mechanism as the primary effector of ethanol vasoconstriction.M oderate-heavy episodic alcohol intake, such as in binge drinking, remains a major public health problem (1, 2). Moderate-heavy drinking is associated, independently of any other factor, with an increased risk for stroke and deaths from ischemic stroke (3, 4). Binge drinkers are significantly predisposed to brain hemorrhage, cerebrovascular spasm, and stroke (3, 5).Cerebrovascular disease associated with moderate-heavy alcohol intake is independent of beverage type and alcohol metabolism but linked to ethanol (EtOH) itself (6, 7). Strong evidence for a dose-response relationship between EtOH intake and risk for stroke suggests causality (8). EtOH cerebral artery constriction is considered responsible for cerebral vasospasm, ischemia, and stroke in moderate-heavy drinkers (6, 9). Acute EtOH at legally intoxicating (Ն20 mM) blood levels in naive subjects constricts cerebral arteries in several species, including humans (7, 9).Rats are excellent models to study EtOH cerebral artery constriction and stroke (7,10,11). Evidence from this and other species indicates that EtOH constricts cerebral arteries by acting primarily on the smooth muscle (7,11,12). However, the molecular mechanisms mediating EtOH cerebral artery constriction remain largely unidentified.In cerebrovascular smooth muscle, an elevation in global intracellular Ca 2ϩ ([Ca 2ϩ ] ic ) leads to contraction (13). Ca 2ϩ mobilization in response to EtOH may result from direct potentiation of mechanisms leading to Ca 2ϩ influx͞release from internal organel...

Ethanol-mediated relaxation of guinea pig urinary bladder smooth muscle: involvement of BK and L-type Ca2+ channels

“…6). The effects of EtOH in high-frequency TBKC DSM cells resemble those previously reported for cerebral arteries (31). In both cell types the amplitudes were decreased; however, the frequency was only attenuated in the vascular myocytes.…”

“…In this tissue, inhibition of BK channels by EtOH mediates this contractile effect, dependent on the presence of the BK channel regulatory ␤ 1 -subunit (6, 7) and also on inhibition of TBKCs due to reduction of Ca 2ϩ sparks and observed direct inhibition of BK channels at high [Ca 2ϩ ] reached during high amplitude TBKCs, estimated to be ϳ10 M (20, 57). As a result, attenuation of the negative feedback loop mediated by BK channels on cerebral artery smooth muscle excitability leads to depolarization, increase in [Ca 2ϩ ] influx, and vasoconstriction (31). In contrast, DSM responded differently to the same concentrations of EtOH by relaxation.…”

“…For example, in hypothalamic-neurohypophysial neurons, acute exposure to EtOH increased BK channel activity, whereas chronic 24-h treatment displayed much weaker effects (47). In cerebral artery smooth muscle cells, acute EtOH exposure in the presence of physiologically relevant high intracellular Ca 2ϩ concentrations ([Ca 2ϩ ]) has been shown to inhibit BK channel activity (6,7,31). In contrast, submicromolar concentrations of intracellular [Ca 2ϩ ] promoted enhancement of BK channel activity (6, 7).…”

Low-dose alcohol actions on α4β3δ GABA A receptors are reversed by the behavioral alcohol antagonist Ro15-4513

“…Other potential alcohol targets that might contribute to Ro15-4513-insensitive acute alcohol actions are NMDA (1), glycine (2), and adenosine receptors (65), and voltage-and Ca 2ϩ -activated (BK) potassium channels (66,67). In addition, we show here that the Ro15-4513-insensitive alcohol action on ␣4␤3␦ GABA A R is abolished by a mutation (␤3N265M) in the ␤3 subunit.…”

Direct Regulation of BK Channels by Phosphatidylinositol 4,5-Bisphosphate as a Novel Signaling Pathway

“…Following endothelium removal and artery pressurization ( Liu et al, 2004 ), vessels were extralumenally perfused with physiological saline solution (Liu et al, 2004) at 3.75 ml/min using a peristaltic pump (Rainin Dynamax RP-1). Drug stock solutions (see below) were diluted in PSS to fi nal concentration.…”