Effect of transverse-tubular chloride conductance on excitability in skinned skeletal muscle fibres of rat and toad
Effect of transverse-tubular chloride conductance on excitability in skinned skeletal muscle fibres of rat and toad
复制标题
DOI：
10.1111/j.1469-7793.1998.551bn.x
复制
发表时间：
1998-06-01
影响因子：
5.5
通讯作者：
Lamb, GD
中科院分区：
文献类型：
--
作者：
Coonan, JR;Lamb, GD
1.由于前人对氯离子电导的研究结论不一致，本研究探讨了横管(T-)系统的氯离子电导对蟾蜍和大鼠骨骼肌纤维膜兴奋性的影响。使用机械剥皮的纤维制剂，在完全去除表面膜后，通过正常的T系统电压传感器机制研究钙离子的释放，从而可以通过力测量来估计T系统的电位。当被剥皮的纤维浸泡在高[K+]溶液中时，封闭的T系统被极化，并可以通过用Na+取代K+来迅速去极化，从而引起肌浆网中的钙离子释放。在大鼠皮肤纤维中，向“肌浆”(即浴液)中加入20 mM的氯离子可部分去极化T系统，导致钙离子释放和随后的电压传感器失活。这些作用可被氯离子通道阻滞剂9-蒽羧酸(9-AC)完全消除。电压传感器失活在肌浆氯-3-20 mM范围内以一种分级的方式增加。在蟾蜍纤维中，电压传感器失活仅在10 mM肌浆氯离子处可检测到，而20 mM氯离子只有在肌浆[K+]降低50%时才能充分去极化T-系统以触发钙离子释放。在蟾蜍纤维中，100 mU M 9-AC几乎不引起T-系统氯离子传导的阻断。研究还发现，当从沐浴在零氯离子细胞外溶液中的肌肉获得去皮纤维时，最初的Na+取代在去极化T系统方面更有效。这与封闭的T-体系中捕获的氯离子对T-体系的电势产生极化效应是一致的。这些结果明确地表明，在大鼠纤维的T-系统中存在较大的9-AC敏感的氯离子电导，而在对9-AC相对不敏感的蟾蜍纤维的T-系统中存在较小但仍可察觉的氯离子电导。这些结果对于了解强直性肌强直中氯通道异常的基础具有重要意义。
1. The influence of the transverse-tubular (T-) system Cl- conductance on membrane excitability in skeletal muscle fibres of toad and rat was examined because of conflicting conclusions of previous studies on Cl- conductance. A mechanically skinned fibre preparation was used that permitted investigation of Ca2+ release via the normal T-system voltage-sensor mechanism after complete removal of the surface membrane, which thereby allowed estimation of the T-system potential from force measurements.2. When a skinned fibre was bathed in a high-[K+] solution, the sealed T-system became polarized and could be rapidly depolarized by replacing the K+ with Na+, thereby eliciting Ca2+ release from the sarcoplasmic reticulum. In rat skinned fibres, addition of 20 mM Cl- to the 'myoplasm' (i.e. bathing solution) partially depolarized the T-system, inducing Ca2+ release and subsequent voltage-sensor inactivation. These effects were completely abolished with 100 mu M of the Cl- channel blocker 9-anthracene carboxylic acid (9-AC). Voltage-sensor inactivation increased in a graded manner over the range 3-20 mM myoplasmic Cl-.3. In toad fibres, voltage-sensor inactivation was only detectable at > 10 mM myoplasmic Cl-, and 20 mM Cl- was only able to depolarize the T-system sufficiently to trigger Ca2+ release if the myoplasmic [K+] was reduced by 50%. In toad fibres, 100 mu M 9-AC caused little if any block of the T-system Cl- conductance.4. It was also found that when skinned fibres were obtained from muscles that had been bathed in a zero Cl- extracellular solution, the initial Na+ substitutions were more effective at depolarizing the T-system. This is consistent with Cl- trapped in the sealed T-system exerting a polarizing effect on T-system potential.5. These results unequivocally demonstrate that there is a large 9-AC-sensitive Cl- conductance in the T-system of rat fibres, and a smaller, though still appreciable, Cl- conductance in the T-system of toad fibres, which is relatively insensitive to 9-AC. The results are important for understanding the basis of the Cl- channel aberration in myotonia.