Ethanol sensitivity of BKCa channels from arterial smooth muscle does not require the presence of the β1-subunit

Ethanol inhibition of large-conductance, Ca2+-activated K+ (BKCa) channels in aortic myocytes may contribute to the direct contraction of aortic smooth muscle produced by acute alcohol exposure. In this tissue, BKCa channels consist of pore-forming ( bslo) and modulatory (β) subunits. Here, modulation of aortic myocyte BKCa channels by acute alcohol was explored by expressing bslo subunits in Xenopus oocytes, in the absence and presence of β1-subunits, and studying channel responses to clinically relevant concentrations of ethanol in excised membrane patches. Overall, average values of bslo channel activity ( NP o, with N = no. of channels present in the patch; P o = probability of a single channel being open) in response to ethanol (3–200 mM) mildly decrease when compared with pre-ethanol, isosmotic controls. However, channel responses show qualitative heterogeneity at all ethanol concentrations. In the majority of patches (42/71 patches, i.e., 59%), a reversible reduction in NP o is observed. In this subset, the maximal effect is obtained with 100 mM ethanol, at which NP o reaches 46.2 ± 9% of control. The presence of β1-subunits, which determines channel sensitivity to dihydrosoyaponin-I and 17β-estradiol, fails to modify ethanol action on bslo channels. Ethanol inhibition of bslo channels results from a marked increase in the mean closed time. Although the voltage dependence of gating remains unaffected, the apparent effectiveness of Ca2+ to gate the channel is decreased by ethanol. These changes occur without modifications of channel conduction. In conclusion, a new molecular mechanism that may contribute to ethanol-induced aortic smooth muscle contraction has been identified and characterized: a functional interaction between ethanol and the bslo subunit and/or its lipid microenvironment, which leads to a decrease in BKCachannel activity.