Cibulsky Susan M, Sather William A
Department of Pharmacology and Program in Neuroscience, University of Colorado Health Sciences Center, Denver 80262, USA.
Biophys J. 2003 Mar;84(3):1709-19. doi: 10.1016/S0006-3495(03)74979-0.
Voltage-gated L-type Ca(2+) channels from cardiac (alpha(1C)) and skeletal (alpha(1S)) muscle differ from one another in ion selectivity and permeation properties, including unitary conductance. In 110 mM Ba(2+), unitary conductance of alpha(1S) is approximately half that of alpha(1C). As a step toward understanding the mechanism of rapid ion flux through these highly selective ion channels, we used chimeras constructed between alpha(1C) and alpha(1S) to identify structural features responsible for the difference in conductance. Combined replacement of the four pore-lining P-loops in alpha(1C) with P-loops from alpha(1S) reduced unitary conductance to a value intermediate between those of the two parent channels. Combined replacement of four larger regions that include sequences flanking the P-loops (S5 and S6 segments along with the P-loop-containing linker between these segments (S5-6)) conferred alpha(1S)-like conductance on alpha(1C). Likewise, substitution of the four S5-6 regions of alpha(1C) into alpha(1S) conferred alpha(1C)-like conductance on alpha(1S). These results indicate that, comparing alpha(1C) with alpha(1S), the differences in structure that are responsible for the difference in ion conduction are housed within the S5-6 regions. Moreover, the pattern of unitary conductance values obtained for chimeras in which a single P-loop or single S5-6 region was replaced suggest a concerted action of pore-lining regions in the control of ion conduction.
来自心脏（α1C）和骨骼肌（α1S）的电压门控L型Ca（2+）通道在离子选择性和通透特性（包括单通道电导）方面彼此不同。在110 mM Ba（2+）中，α1S的单通道电导约为α1C的一半。作为理解离子通过这些高选择性离子通道快速通量机制的第一步，我们使用了在α1C和α1S之间构建的嵌合体来确定导致电导差异的结构特征。用α1S的P环联合替换α1C中的四个孔衬里P环，使单通道电导降低到两个亲本通道之间的中间值。联合替换包括P环侧翼序列（S5和S6片段以及这些片段之间含P环的连接子（S5-6））的四个更大区域，赋予α1C类似α1S的电导。同样，将α1C的四个S5-6区域替换到α1S中，赋予α1S类似α1C的电导。这些结果表明，与α1S相比，α1C中导致离子传导差异的结构差异存在于S5-6区域内。此外，对于单个P环或单个S5-6区域被替换的嵌合体获得的单通道电导值模式表明，孔衬里区域在离子传导控制中协同作用。
