Vogalis F, Vincent T, Qureshi I, Schmalz F, Ward M W, Sanders K M, Horowitz B
Department of Physiology, University of Nevada School of Medicine, Reno 89557, USA.
Am J Physiol. 1996 Oct;271(4 Pt 1):G629-39. doi: 10.1152/ajpgi.1996.271.4.G629.
We have cloned cDNAs encoding the alpha- and beta-subunits of a large-conductance Ca(2+)-activated K+ channel (BK channel) from canine colonic smooth muscle (cslo-alpha and cslo-beta). Nucleotide sequence homology of cslo-alpha with mslo and dslo suggests that it is the canine homologue of these genes. The carboxy-terminal end of the protein is the most diverse between species, and we have also found alternative exons in cslo-alpha in this region. We have identified a unique splice site in the carboxy-terminal region of cslo-alpha, which we term site 5. Northern analysis demonstrates expression of both alpha- and beta-subunits in all canine vascular and visceral smooth muscles tested. Expression of alpha-1 alone and alpha + beta-subunit cRNA in Xenopus oocytes results in a Ca(2+)- and voltage-dependent conductance. The activity of alpha/beta-channels, measured as either changes in the voltage of half-maximal activation (V0.5) in open probability (NP0) or in the normalized conductance (G/Cmax), was more sensitive to [Ca2+]free than channels composed of the alpha-subunit alone. Neither alpha- nor alpha/beta-channels expressed in membrane patches of Xenopus oocytes were found to be regulated by protein kinase G.
我们已经从犬结肠平滑肌中克隆出编码大电导钙激活钾通道（BK通道）α和β亚基的cDNA（cslo-α和cslo-β）。cslo-α与mslo和dslo的核苷酸序列同源性表明它是这些基因的犬类同源物。蛋白质的羧基末端在不同物种间差异最大，我们还在该区域的cslo-α中发现了可变外显子。我们在cslo-α的羧基末端区域鉴定出一个独特的剪接位点，我们将其命名为位点5。Northern分析表明，在所有测试的犬类血管和内脏平滑肌中均有α和β亚基的表达。单独表达α-1以及在非洲爪蟾卵母细胞中表达α + β亚基cRNA会产生钙和电压依赖性电导。以半数最大激活电压（V0.5）、开放概率（NP0）或归一化电导（G/Cmax）的变化来衡量，α/β通道的活性比仅由α亚基组成的通道对无钙状态更敏感。在非洲爪蟾卵母细胞膜片中表达的α通道和α/β通道均未发现受蛋白激酶G调节。
