Interspecies and regional variability of alcohol action on large cerebral arteries: regulation by KCNMB1 proteins

Abstract

Alcohol intake leading to blood ethanol concentrations (BEC) ≥ legal intoxication modifies brain blood flow with increases in some regions and decreases in others. Brain regions receive blood from the Willis' circle branches: anterior, middle (MCA) and posterior cerebral (PCA), and basilar (BA) arteries. Rats and mice have been used to identify the targets mediating ethanol-induced effects on cerebral arteries, with conclusions being freely interchanged, albeit data were obtained in different species/arterial branches. We tested whether ethanol action on cerebral arteries differed between male rat and mouse and/or across different brain regions, and identified the targets of alcohol action. In both species and all Willis' circle branches, ethanol evoked reversible and concentration-dependent constriction (EC50s≈37-86 mM; below lethal BEC in alcohol-naïve humans). While showing similar constriction to depolarization, both species displayed differential responses to ethanol: in mice, MCA constriction was highly sensitive to the presence/absence of the endothelium, while rat PCA was significantly more sensitive to ethanol than its mouse counterpart. In rat, but not mouse, BA was more ethanol-sensitive than other branches. Both interspecies and regional variability were ameliorated by endothelium. Selective BK channel block in de-endothelialized vessels demonstrated that these channels were the effectors of alcohol-induced cerebral artery constriction across regions and species. Variabilities in alcohol actions did not fully matched KCNMB1 expression across vessels. However, immunofluorescence data from KCNMB1-/- mouse arteries electroporated with KCNMB1-coding cDNA demonstrate that KCNMB1 proteins, which regulate SM BK channel function and vasodilation, regulate interspecies and regional variability of brain artery responses to alcohol.

Alcohol and pregnenolone interaction on cerebral arteries through targeting of vascular smooth muscle Ca2+- and voltage-gated K+ channels of big conductance

“…As found with males, MCA constriction in females under exposure to EtOH and PREG was characterized by loss of synergism when PREG was probed at maximally effective concentrations (10 and 100 μM; [ 19 ]) ( Figure 2D ). Since it has been documented by us and others, both in this system and under identical conditions, that depolarizing 60 mM KCl constricts MCA by >20% in both males and females (see [ 28 ] and references cited therein), the lack of synergism between PREG and EtOH in evoking MCA constriction cannot be explained by a “ceiling effect” (i.e., by MCA segments reaching their maximal possible degree of constriction). Therefore, the synergism between EtOH and PREG at submaximal concentrations and the loss of synergism when either EC Max is reached on isolated, de-endothelialized MCA segments indicate that the two drugs converge on a common pathway or target(s), likely located in the vascular SM itself.…”

“…Indeed, alterations in normal control of cerebral artery diameter play a significant role in the pathophysiology of vascular dementia, migraines, seizures, and cerebral vasospasm [ 51 – 53 ]. While (i) the constriction of cerebral arteries by toxicologically relevant concentrations of EtOH has been widely reported in several species, including humans ([ 28 ] and references therein), and (ii) the constriction of cerebral arteries by therapeutically relevant concentrations of PREG has been previously reported by our group [ 19 ], the current study is the first to determine the effect of PREG combined with EtOH on cerebral artery diameter. The data clearly demonstrate that submaximal vasoconstrictive concentrations of PREG (subµM), i.e., concentrations equivalent to those found in the blood in humans following administration of PREG supplements, are able to potentiate the constriction of cerebral arteries (MCAs) by 50 mM EtOH ( Figure 2 ).…”

“…For the testing of PREG, a concentration of 10 μM was chosen because this constitutes the lowest PREG concentration that is able to evoke maximal constriction of the mouse MCA in vitro and in vivo (EC max ) [ 19 ]. For EtOH, 50 mM was chosen because this concentration is reached in blood circulation after a moderate-to-heavy alcohol consumption episode and is close to EC max for ethanol for constriction of mouse cerebral arteries that branch out of Willis’ circle, including the MCA [ 28 ]. In contrast to the controls, bolus injections of either PREG or EtOH administered to male animals resulted in 28% ± 3.8% and 31.2% ± 2.1% reductions in artery diameter, respectively ( Figure 1 ).…”

“…Given the involvement of BK channels in EtOH- [ 25 , 28 , 29 ] and PREG-induced [ 19 ] constriction of de-endothelialized cerebral arteries, we next probed whether these channels were involved in MCA constriction by PREG or EtOH when these agents were applied in combination vs. separately. Synergism in MCA constriction was not detected either in males or in females when EtOH was probed at 75 mM ( Figures 2E, F ), extending our findings shown in Figures 2C, D .…”

“…Ethanol (EtOH) at concentrations reached in the blood during binge drinking constricts cerebral arteries in a wide variety of species, including humans, both in vivo and in vitro [ 21 – 28 ]. This EtOH action is independent of circulating and endothelial factors; instead, it results from inhibition of the Ca 2+ - and voltage-gated K + large conductance channels (BK channels) present in cerebrovascular smooth muscle (SM) [ 29 ].…”