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

Abstract

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, Ca 2ϩ -activated K ϩ (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 ϭ no. of channels present in the patch; Po ϭ 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 Ϯ 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 Ca 2ϩ 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 BK Ca channel activity. maxi-potassium channel; alcohol; aorta; vasoconstriction ACUTE EXPOSURE TO clinically relevant concentrations of ethanol (EtOH) causes contraction of peripheral, cerebral, coronary, and umbilical arteries in several species, including humans (2-4, 23). There is substantial evidence that EtOH produces vasocontriction by acting on the smooth muscle itself (2,26,35,55). However, the ion channel populations involved in EtOH action are largely unknown.

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

“…EtOH is a more effective inhibitor of bslo channels in excised patches as internal [Ca 2ϩ ] is increased (17). In addition, EtOH activates mslo channels at submicromolar internal [Ca 2ϩ ] but inhibits activity when [Ca 2ϩ ] ic is Ն3 M (18).…”

“…EtOH decreases the activity of aortic smooth muscle BK channels reconstituted into lipid bilayers (16) and BK pore-forming bslo subunits expressed in oocytes (17). However, EtOH inhibition of BK channels is not universal, because both channel activation (18,19) and refractoriness (20) were observed.…”

“…Thus, EtOH action on channels heterologously expressed may differ dramatically from drug action on the native channel studied in intact cerebrovascular myocytes. In particular, EtOH modulation of BK channel activity is a function of internal [Ca 2ϩ ] (17,18). Thus, it becomes critical to determine any possible modulatory role of EtOH on BK channels in intact myocytes where Ca 2ϩ sparks regulate [Ca 2ϩ ] near the BK channel and, thus, channel activity.…”

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

“…Solutions were made with deionized (18 M Ω .cm) water and high-grade purity salts. Free Ca 2+ concentrations were calculated using Max Chelator Sliders (C. Patton, Stanford University, Stanford, CA) and validated experimentally ( Dopico, 2003 ). A variety of solutions were used, as follows.…”

The residue I257 at S4–S5 linker in KCNQ1 determines KCNQ1/KCNE1 channel sensitivity to 1-alkanols

“…Biochemical and electrophysiological approaches have demonstrated the presence of ethanol-binding sites in various ion channel proteins, but there remains a considerable debate regarding the putative binding sites due to a lack of 3D structural data [7,8,24] . Ethanol has been reported to affect the human heart rate [25,26] . KCNQ1 and KCNE1 form a complex in human ventricular cardiomyocytes and are involved in recharging the cardiac muscle after each heartbeat to maintain a regular rhythm.…”