Chua M, Betz W J
Department of Physiology, University of Colorado Health Sciences Center 80262.
Biophys J. 1991 Jun;59(6):1251-60. doi: 10.1016/S0006-3495(91)82340-2.
The channels present on the surface membrane of isolated rat flexor digitorum brevis muscle fibers were surveyed using the patch clamp technique. 85 out of 139 fibers had a novel channel which excluded the anions chloride, sulfate, and isethionate with a permeability ratio of chloride to sodium of less than 0.05. The selectivity sequence for cations was Na+ = K+ = Cs+ greater than Ca++ = Mg++ greater than N-Methyl-D-Glucamine. The channel remained closed for long periods, and had a large conductance of approximately 320 pS with several subconductance states at approximately 34 pS levels. Channel activity was not voltage dependent and the reversal potential for cations in muscle fibers of approximately 0 mV results in the channel's behaving as a physiological leakage conductance. Voltage activated potassium channels were present in 65 of the cell attached patches and had conductances of mostly 6, 12, and 25 pS. The voltage sensitivity of the potassium channels was consistent with that of the delayed rectifier current. Only three patches contained chloride channels. The scarcity of chloride channels despite the known high chloride conductance of skeletal muscle suggests that most of the chloride channels must be located in the transverse tubular system.
采用膜片钳技术对分离的大鼠趾短屈肌纤维表面膜上的通道进行了研究。139根纤维中有85根具有一种新型通道，该通道排斥氯离子、硫酸根离子和羟乙基磺酸根离子，氯与钠的通透率小于0.05。阳离子的选择性顺序为Na+ = K+ = Cs+＞Ca++ = Mg++＞N-甲基-D-葡萄糖胺。该通道长时间保持关闭状态，具有大约320 pS的大电导，在大约34 pS水平有几个亚电导状态。通道活性不依赖电压，在肌肉纤维中阳离子的反转电位约为0 mV，导致该通道表现为生理性漏电导。在65个细胞贴附膜片中存在电压激活钾通道，其电导大多为6、12和25 pS。钾通道的电压敏感性与延迟整流电流的一致。只有3个膜片含有氯通道。尽管已知骨骼肌具有高氯电导，但氯通道的稀缺表明大多数氯通道必定位于横管系统中。
