Unitary behavior of skeletal, cardiac, and chimeric L-type Ca2+ channels expressed in dysgenic myotubes
Unitary behavior of skeletal, cardiac, and chimeric L-type Ca2+ channels expressed in dysgenic myotubes
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DOI：
10.1085/jgp.107.6.731
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发表时间：
1996-06-01
影响因子：
3.8
通讯作者：
Beam, KG
中科院分区：
文献类型：
--
作者：
Dirksen, RT;Beam, KG
骨骼肌和心脏二氢吡啶受体既作为电压依赖性L-型钙通道（L-通道）发挥作用，又作为触发肌浆网钙释放的关键蛋白质发挥作用。尽管有这些相似之处，骨骼L-通道表现出明显慢于心脏L-通道的激活速率。我们通过比较表达骨骼、心脏或嵌合二氢吡啶受体的发育不良肌管细胞贴附斑块中L通道的单一行为，研究了这种差异的机制。我们的研究结果表明，合奏平均激活迅速为纯粹的心脏二氢吡啶受体和约5倍更慢的L-通道归因于纯粹的骨骼二氢吡啶受体或嵌合二氢吡啶受体，其中只有第一个内部重复序列和所有推定的细胞内循环的骨骼起源。所有的结构研究同样表现出一个简短的（2毫秒）和一个长（大于或等于15毫秒）的开放时间在湾K 8644的存在下，这两个依赖于电压显着。在湾K 8644的情况下，总的开放事件的分数显着转移到较短的开放时间，而不改变合奏激活率。具有心脏样快速激活的L通道的关闭时间分析（在二氢吡啶激动剂存在下记录）揭示了短暂（类似于1-ms）关闭时间和第二个电压依赖性持久关闭时间。快速激活L-通道去极化后第一次开放的时间比缓慢激活L-通道快三至六倍，并且强烈依赖于两种类型通道的电压。结果表明，心脏L-通道中快速而骨骼L-通道中缓慢的电压依赖性闭合-闭合转换可以解释这两个通道之间激活速率的差异。
Skeletal and cardiac dihydropyridine receptors function both as voltage-dependent L-type calcium channels (L-channels) and as critical proteins that trigger calcium release from the sarcoplasmic reticulum in muscle. In spite of these similarities, skeletal L-channels exhibit a markedly slower activation rate than cardiac L-channels. We investigated the mechanisms underlying this difference by comparing the unitary behavior of L-channels in cell-attached patches of dysgenic myotubes expressing skeletal, cardiac, or chimeric dihydropyridine receptors. Our results demonstrate that ensemble averages activate rapidly for the purely cardiac dihydropyridine receptor and approximately five times more slowly for L-channels attributable to the purely skeletal dihydropyridine receptor or a chimeric dihydropyridine receptor in which only the first internal repeat and all of the putative intracellular loops are of skeletal origin. All of the constructs studied similarly exhibit a brief (2-ms) and a long (greater than or equal to 15-ms) open time in the presence of Bay K 8644, neither of which depend significantly on voltage. In the absence of Bay K 8644, the fraction of total open events is markedly shifted to the briefer open time without altering the rate of ensemble activation. Closed time analysis of L-channels with cardiac-like, rapid activation (recorded in the presence of dihydropyridine agonist) reveals both a brief (similar to 1-ms) closed time and a second, voltage-dependent, long-lasting closed time. The time until first opening after depolarization is three to six times faster for rapidly activating L-channels than for slowly activating L-channels and depends strongly on voltage for both types of channels. The results suggest that a voltage-dependent, closed-closed transition that is fast in cardiac L-channels and slow in skeletal L-channels can account for the difference in activation rate between these two channels.