Qu Y, Campbell D L
Department of Pharmacology, Duke University Medical Center, Durham, NC 27710, USA.
Can J Cardiol. 1998 Feb;14(2):263-72.
The gigaohm seal patch clamp (whole cell configuration) and an internal perfusion technique were used to study the effects of sarcoplasmic reticulum (SR) calcium release on L-type calcium current (ICa,L) in ferret enzymatically isolated right ventricular myocytes. ICa,L (22 to 24 degrees C) was isolated by using various sodium- and potassium-free salines, which eliminated or greatly minimized activation of the sodium-calcium exchanger and calcium-activated cation and anion currents. When calcium was the charge carrier, inactivation of ICa,L was nonmonotonic in many myocytes; after an early rapid phase of inactivation, a secondary inward 'hump' component was frequently observed between -40 to -10 mV. The hump component was not present when barium replaced calcium but was observed when calcium carried the current in low intracellular (aspartate) and extracellular (methanesulphonate) chloride solutions. When BAPTA 10 mM was perfused internally the amplitude of ICa,L increased, the kinetics of inactivation slowed and the hump component disappeared. Both caffeine 10 mM and ryanodine 10 microM increased the amplitude of ICa,L in the hyperpolarized range of potentials (negative to 0 mV), slowed the kinetics of ICa,L inactivation and caused the hump component to disappear. Under current clamp mode, both caffeine and ryanodine significantly prolonged the duration of the action potential. Taken in aggregate, preliminary data demonstrate that, in ferret right ventricular myocytes, a secondary inward hump component can be frequently observed after the early rapid phase of inactivation of ICa,L, causing the net inward current to display biphasic, nonmonotonic behaviour. This secondary inward hump current is only present when calcium is the charge carrier, is absent when BAPTA is used as an intracellular calcium chelator and SR calcium release is disrupted by either caffeine or ryanodine, and is not due to activation of either the sodium-calcium exchanger or various putative calcium-activated cation or anion channels. Rather, preliminary results strongly suggest that this secondary inward hump current component is due to modulation of ICa,L by SR calcium release. Possible physiological and theoretical implications of the results are discussed briefly.
采用千兆欧封接膜片钳技术（全细胞模式）和内部灌流技术，研究雪貂酶解分离的右心室肌细胞中肌浆网（SR）钙释放对L型钙电流（ICa,L）的影响。通过使用各种无钠和无钾盐溶液分离ICa,L（22至24摄氏度），这些溶液消除或极大地减少了钠钙交换体以及钙激活阳离子和阴离子电流的激活。当钙作为电荷载体时，许多心肌细胞中ICa,L的失活是非单调的；在早期快速失活阶段之后，经常在-40至-10 mV之间观察到一个次级内向“驼峰”成分。当钡替代钙时，驼峰成分不存在，但当钙在低细胞内（天冬氨酸）和细胞外（甲磺酸盐）氯化物溶液中携带电流时可观察到。当内部灌流10 mM BAPTA时，ICa,L的幅度增加，失活动力学减慢，驼峰成分消失。10 mM咖啡因和10 μM雷诺丁均增加了超极化电位范围（负至0 mV）内ICa,L的幅度，减慢了ICa,L失活的动力学，并使驼峰成分消失。在电流钳模式下，咖啡因和雷诺丁均显著延长了动作电位的持续时间。总体而言，初步数据表明，在雪貂右心室肌细胞中，在ICa,L早期快速失活阶段之后，经常可观察到一个次级内向驼峰成分，导致内向净电流呈现双相、非单调行为。这种次级内向驼峰电流仅在钙作为电荷载体时存在，当使用BAPTA作为细胞内钙螯合剂且SR钙释放被咖啡因或雷诺丁破坏时不存在，并且不是由于钠钙交换体或各种假定的钙激活阳离子或阴离子通道的激活所致。相反，初步结果强烈表明，这种次级内向驼峰电流成分是由于SR钙释放对ICa,L的调节。简要讨论了结果可能的生理和理论意义。
