Bukiya Anna N, Vaithianathan Thirumalini, Toro Ligia, Dopico Alejandro M
Department of Pharmacology, University of Tennessee HSC, 874 Union Ave, Memphis, TN 38163, USA.
Biochem Biophys Res Commun. 2009 Dec 18;390(3):995-1000. doi: 10.1016/j.bbrc.2009.10.091. Epub 2009 Oct 21.
Large conductance, calcium- and voltage-gated potassium (BK) channels regulate numerous physiological processes. While most basic functional characteristics of native BK channels are reproduced by BK alpha (slo1) subunit homotetramers, key biophysical and pharmacological properties are drastically modified by the presence of auxiliary beta subunits (encoded by KCNMB1-4). Numerous physiological steroids, including sex hormones, gluco- and mineralocorticoids, activate beta subunit-containing BK channels, yet these steroids appear to be sensed by different types of beta subunits, with some steroids being sensed by homomeric slo1 channels as well. We recently showed that beta1 sensitizes the BK channel to microM concentrations of lithocholate (LC). Following expression of rat cerebral artery myocyte slo1 subunits ("cbv1") with beta1, beta2, beta3 or beta4 in Xenopus laevis oocytes we now demonstrate that BK beta2, beta3 and beta4 subunits fail to substitute for beta1 in providing LC-sensitivity (150 microM) to the BK channel. These findings document for the first time a rather selective steroid activation of BK channels via a particular channel accessory subunit. In addition, LC routinely activated native BK channels in myocytes freshly isolated from rat cerebral artery smooth muscle, where BK beta1 is highly expressed, while failing to do so in skeletal (flexor digitorum brevis) muscle, where BK beta1 expression is negligible. This indicates that the native environment of the BK channel sustains the LC-sensitivity distinctly provided to the BK channel by beta1 subunits. Our study indicates that LC represents a unique tool to probe the presence of functional beta1-subunits and selectively activate BK channels in tissues that highly express KCNMB1.
大电导钙和电压门控钾（BK）通道调节众多生理过程。虽然天然BK通道的大多数基本功能特性可由BKα（slo1）亚基同四聚体重现，但关键的生物物理和药理学特性会因辅助β亚基（由KCNMB1 - 4编码）的存在而发生显著改变。许多生理类固醇，包括性激素、糖皮质激素和盐皮质激素，可激活含β亚基的BK通道，然而这些类固醇似乎由不同类型的β亚基感知，有些类固醇也可被同聚体slo1通道感知。我们最近发现β1使BK通道对微摩尔浓度的石胆酸（LC）敏感。在非洲爪蟾卵母细胞中表达大鼠脑动脉肌细胞slo1亚基（“cbv1”）与β1、β2、β3或β4后，我们现在证明BKβ2、β3和β4亚基无法替代β1为BK通道提供LC敏感性（150微摩尔）。这些发现首次证明了通过特定通道辅助亚基对BK通道进行相当选择性的类固醇激活。此外，LC常规激活从大鼠脑动脉平滑肌新鲜分离的肌细胞中的天然BK通道，其中BKβ1高度表达，而在BKβ1表达可忽略不计的骨骼肌（趾短屈肌）中则不能激活。这表明BK通道的天然环境维持了由β1亚基赋予BK通道的独特LC敏感性。我们的研究表明，LC是一种独特的工具，可用于探测功能性β1亚基的存在，并在高表达KCNMB1的组织中选择性激活BK通道。
