Ethanol sensitivity of BKCa channels from arterial smooth muscle does not require the presence of the 1-subunit

Dopico, Alejandro M. Ethanol sensitivity of BKCa channels from arterial smooth muscle does not require the presence of the 1-subunit. Am J Physiol Cell Physiol 284: C1468–C1480, 2003. First published February 5, 2003; 10.1152/ajpcell.00421.2002.—Ethanol inhibition of largeconductance, 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 ( ) 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 1-subunits, and studying channel responses to clinically relevant concentrations of ethanol in excised membrane patches. Overall, average values of bslo channel activity (NPo, with N no. of channels present in the patch; Po 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 NPo is observed. In this subset, the maximal effect is obtained with 100 mM ethanol, at which NPo reaches 46.2 9% of control. The presence of 1-subunits, which determines channel sensitivity to dihydrosoyaponin-I and 17 -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 BKCa channel activity.