Tang Q Y, Qi Z, Naruse K, Sokabe M
Department of Physiology, Nagoya University Graduate School of Medicine, Nagoya 466-8550, Japan.
J Membr Biol. 2003 Dec 1;196(3):185-200. doi: 10.1007/s00232-003-0637-8.
We have characterized electrophysiological and pharmacological properties of a stretch-activated BKca channel (SAKcaC) that was cloned from cultured chick ventricular myocytes (CCVM) and expressed in chinese hamster ovary cells (CHO) using the patch-clamp technique. Our results indicate that the cloned SAKcaC keeps most of the key properties of the native SAKcaC in CCVM, such as conductance, ion selectivity, pressure-, voltage- and Ca(2+)-dependencies. However, there was a slight difference between these channels in the effects of channel blockers, charybdotoxin (CTX) and gadolinium (Gd(3+)). The native SAKcaC was blocked in an all-or-none fashion characterized as the slow blockade, whereas the conductance of the cloned SAKcaC was gradually decreased with the blockers' concentration, without noticeable blocking noise. As the involvement of some auxiliary components was suspected in this difference, we cloned a BK beta-subunit from CCVM and coexpressed it with the cloned SAKcaC in CHO cells to examine its effects on the SAKcaC. Although the pharmacological properties of the cloned SAKcaC turned out to be very similar to the native one by the coexpression, it also significantly altered the key characteristics of SAKcaC, such as voltage- and Ca(2+)-dependencies. Therefore we concluded that the native SAKca in CCVM does not interact with the corresponding endogenous beta-subunit. The difference in pharmacological properties between the expressed SAKcaC in CHO and the native one in CCVM suggests that the native SAKca in CCVM is modulated by unknown auxiliary components.
我们利用膜片钳技术对从培养的鸡心室肌细胞（CCVM）中克隆并在中国仓鼠卵巢细胞（CHO）中表达的一种牵张激活的大电导钙激活钾通道（SAKcaC）的电生理和药理学特性进行了表征。我们的结果表明，克隆的SAKcaC保留了CCVM中天然SAKcaC的大部分关键特性，如电导、离子选择性、压力依赖性、电压依赖性和Ca(2+)依赖性。然而，这些通道在通道阻断剂、蝎毒素（CTX）和钆（Gd(3+)）的作用方面存在细微差异。天然SAKcaC以全或无的方式被阻断，其特征为缓慢阻断，而克隆的SAKcaC的电导随阻断剂浓度逐渐降低，且无明显的阻断噪声。由于怀疑这种差异涉及一些辅助成分，我们从CCVM中克隆了一个BKβ亚基，并将其与克隆的SAKcaC在CHO细胞中共表达，以研究其对SAKcaC的影响。尽管通过共表达发现克隆的SAKcaC的药理学特性与天然的非常相似，但它也显著改变了SAKcaC的关键特性，如电压依赖性和Ca(2+)依赖性。因此我们得出结论，CCVM中的天然SAKca不与相应的内源性β亚基相互作用。CHO中表达的SAKcaC与CCVM中天然的SAKcaC在药理学特性上的差异表明，CCVM中的天然SAKca受到未知辅助成分的调节。
