Mazzanti M, DeFelice L J
Department of Anatomy and Cell Biology, Emory University, Atlanta, Georgia 30322.
Biophys J. 1988 Dec;54(6):1139-48. doi: 10.1016/S0006-3495(88)83048-0.
By averaging the current that passes through cell-attached patches on beating heart cells, while measuring action potentials with a whole-cell electrode, we were able to study K channels during beating. In 7-d chick ventricle in 1.3 mM K physiological solutions at room temperature, delayed-rectifier channels have three linear conductance states: 60, 30, and 15 pS. The 60 and 15 pS conductances can exist alone, but all three states may appear in the same patch as interconverting conductance levels. The delayed-rectifier conductance states have low densities (less than 10 channels per 10-microns diam cell), and all have a reversal potential near -75 mV and the same average kinetics. Outward K current through delayed-rectifier channels follows the upstroke without appreciable delay and lasts throughout the action potential. No inward current flows through delayed-rectifier channels during beating. The early outward channel has a nonlinear conductance of 18-9 pS depending on the potential. It also turns on immediately after the upstroke of the action potential and lasts on average only 50 ms. The early outward channel has an extrapolated reversal potential near -30 mV; no inward current flows during beating. The inward-rectifier has an extrapolated conductance and reversal potential of 2-3 pS and -80 mV in 1.3 mM K. Channel kinetics are independent of external K between 10 and 120 mM, and the channel conducts current only during the late repolarization and diastolic phases of the action potential. No outward current flows through inward-rectifier channels during beating. This work parallels a previous study of Na channels using similar techniques (Mazzanti, M., and L. J. DeFelice. 1987, Biophys. J. 52:95-100).
通过在测量全细胞电极动作电位的同时，对通过跳动心脏细胞上细胞贴附膜片的电流进行平均，我们能够研究跳动过程中的钾通道。在室温下1.3 mM钾的生理溶液中培养7天的鸡心室中，延迟整流通道有三种线性电导状态：60、30和15 pS。60和15 pS的电导可以单独存在，但这三种状态可能会在同一膜片中以相互转换的电导水平出现。延迟整流电导状态的密度较低（每10微米直径的细胞中少于10个通道），并且都具有接近 -75 mV的反转电位和相同的平均动力学。通过延迟整流通道的外向钾电流在动作电位上升支后无明显延迟地跟随，并持续整个动作电位过程。在跳动过程中没有内向电流通过延迟整流通道。早期外向通道的非线性电导根据电位在18 - 9 pS之间。它也在动作电位上升支后立即开启，平均仅持续50毫秒。早期外向通道的外推反转电位接近 -30 mV；在跳动过程中没有内向电流通过。内向整流器在1.3 mM钾中的外推电导和反转电位分别为2 - 3 pS和 -80 mV。通道动力学在10至120 mM的外部钾浓度范围内与外部钾无关，并且该通道仅在动作电位的晚期复极化和舒张期传导电流。在跳动过程中没有外向电流通过内向整流通道。这项工作与先前使用类似技术对钠通道的研究（Mazzanti, M., and L. J. DeFelice. 1987, Biophys. J. 52:95 - 100）相似。
