Hymel L, Striessnig J, Glossmann H, Schindler H
Institute for Biophysics, University of Linz, Austria.
Proc Natl Acad Sci U S A. 1988 Jun;85(12):4290-4. doi: 10.1073/pnas.85.12.4290.
The purified 1,4-dihydropyridine receptor from skeletal muscle has been incorporated into planar bilayers, and its channel characteristics have been investigated. Conductances showed the characteristics of an L-type Ca2+ channel: divalent cation selectivity (PBa/PNa approximately equal to 30), blockage of Na+ conductance by micromolar Ca2+, and blockage of the Ca2+ channel by D890 and by Cd2+. The alpha 1 subunit of the receptor must be phosphorylated by the cAMP-dependent protein kinase to give channel activity. BAY K 8644 did not activate nonphosphorylated channels, and (+)-PN200-110 caused dramatic prolongation of mean open times when applied after phosphorylation. Channel properties were found to be dependent on association of receptor molecules in the bilayer. Single receptor molecules form channels of 0.9 pS (100 mM Ba2+) and show no voltage-dependent gating. Upon association, both voltage-dependent gating and higher conductance events are recovered; stabilized conductance levels assume values of even multiples of 0.9 pS, predominately 7.5 and 15 pS and multiples of these values up to 60 pS. Thus, individual channels become functionally coupled (synchronous opening and closing) with association, reinstating the characteristics of one larger unitary channel. It is concluded that the L-type Ca2+ channel represents an oligomer of 1,4-dihydropyridine-receptor protein complexes, each of which constitutes a channel, where the array of channels (oligochannel) opens and closes in concerted action.
从骨骼肌中纯化得到的1,4 - 二氢吡啶受体已被整合到平面双层膜中，并对其通道特性进行了研究。电导显示出L型Ca2+通道的特性：二价阳离子选择性（PBa/PNa约等于30），微摩尔浓度的Ca2+可阻断Na+电导，D890和Cd2+可阻断Ca2+通道。受体的α1亚基必须被cAMP依赖性蛋白激酶磷酸化才能产生通道活性。BAY K 8644不能激活未磷酸化的通道，而(+)-PN200 - 110在磷酸化后应用时会显著延长平均开放时间。发现通道特性取决于双层膜中受体分子的缔合。单个受体分子形成0.9 pS（100 mM Ba2+）的通道，且不显示电压依赖性门控。缔合后，电压依赖性门控和更高的电导事件均得以恢复；稳定的电导水平呈现0.9 pS的偶数倍数值，主要为7.5和15 pS以及这些值的倍数直至60 pS。因此，单个通道通过缔合在功能上耦合（同步开放和关闭），恢复了一个更大的单一通道的特性。结论是，L型Ca2+通道代表1,4 - 二氢吡啶受体蛋白复合物的寡聚体，其中每个复合物构成一个通道，通道阵列（寡通道）协同开放和关闭。
