Buljubasic N, Marijic J, Kampine J P, Bosnjak Z J
Department of Anesthesiology, Medical College of Wisconsin, Milwaukee 53226.
Can J Physiol Pharmacol. 1994 Mar;72(3):189-98. doi: 10.1139/y94-030.
This study characterizes K+ current in canine coronary artery and investigates its role in regulation of vascular smooth muscle tone during the resting and activated state. Isolated rings and whole-cell K+ current as well as single K+ channels were studied. Tetraethylammonium (< 3 mM) did not increase the resting tension in isolated rings; however, 0.3 mM tetraethylammonium increased tension in vessels that were precontracted by elevated [K+]o or 5-hydroxytryptamine (5-HT). The whole-cell K+ current showed voltage and Ca2+ dependency and sensitivity to tetraethylammonium (31 +/- 7, 72 +/- 2, and 83 +/- 4% depression by 1, 10, and 30 mM tetraethylammonium, respectively). A large-conductance (100 pS) K+ channel was identified in cell-attached patches with open-time distribution fitted with two exponentials. Calcium ionophore A23187 (10 microM) increased the probability of opening, mean open time, and amplitude of this channel in cell-attached patches, suggesting Ca2+ dependency. A23187 shifted the plot of unitary current as a function of pipette potential to the right, suggesting A23187-induced cell hyperpolarization. In inside-out patches, increase in cytoplasmic-side [Ca2+] from 10(-7) to 10(-6) M increased both the frequency of channel opening and duration of the open state, without changing its conductance. Tetraethylammonium (1 mM) on the cytoplasmic side caused a reversible decrease in the current amplitude. Charybdotoxin (100 nM) decreased the probability of opening and mean open time and increased mean closed time, while apamin (100 nM) did not significantly affect channel kinetics. In summary, this study demonstrates the existence and important functional role of a large-conductance, Ca(2+)-sensitive K+ channel in regulation of membrane potential and cell excitability, as well as some aspects of regulation and kinetics of this channel in canine coronary arterial cells.
本研究对犬冠状动脉中的钾离子电流进行了表征，并研究了其在静息和激活状态下对血管平滑肌张力调节中的作用。研究了分离的血管环、全细胞钾离子电流以及单个钾离子通道。四乙铵（<3 mM）不会增加分离血管环的静息张力；然而，0.3 mM四乙铵会增加由升高的细胞外钾离子浓度（[K+]o）或5-羟色胺（5-HT）预收缩的血管的张力。全细胞钾离子电流表现出电压和钙离子依赖性以及对四乙铵的敏感性（分别用1、10和30 mM四乙铵处理后，电流抑制率分别为31±7%、72±2%和83±4%）。在细胞贴附式膜片上鉴定出一种大电导（100 pS）的钾离子通道，其开放时间分布符合两个指数函数。钙离子载体A23187（10 μM）增加了细胞贴附式膜片中该通道的开放概率、平均开放时间和幅度，表明其具有钙离子依赖性。A23187将单位电流与微电极电位关系曲线向右移动，表明A23187诱导细胞超极化。在内外翻式膜片中，细胞质侧钙离子浓度从10⁻⁷ M增加到10⁻⁶ M会增加通道开放频率和开放状态持续时间，而不改变其电导。细胞质侧的1 mM四乙铵会使电流幅度可逆性降低。蝎毒素（100 nM）降低了开放概率和平均开放时间，并增加了平均关闭时间，而蜂毒明肽（100 nM）对通道动力学没有显著影响。总之，本研究证明了一种大电导、钙离子敏感的钾离子通道在调节膜电位和细胞兴奋性方面的存在及其重要功能作用，以及该通道在犬冠状动脉细胞中的一些调节和动力学方面的特性。
