Loirand G, Pacaud P, Baron A, Mironneau C, Mironneau J
Laboratoire de Physiologie Cellulaire et Pharmacologie Moléculaire CJF INSERM 88-13, Bordeaux, France.
Z Kardiol. 1991;80 Suppl 7:59-63.
A rapid transient rise in the free cytosolic Ca2+ concentration is one of the earliest events in smooth muscle cell activation and is involved in the opening of several classes of Ca2(+)-sensitive ion channels such as K+ channels and Cl- channels. In portal vein smooth muscle cells, in addition to the Ca(2+)-dependent Cl-current, single-channel activities were recorded in response to external application of 10 mM caffeine, in the absence of EGTA in the pipette solution. The conductance of this novel type of channel was around 200 pS for membrane potentials ranging between -100 to +60 mV. The single-channel activities were also induced by external application of noradrenaline (10(-5) M) or acetylcholine (10(-5) M), by Ca2+ entry through voltage-dependent Ca(2+)-channels, and by intracellular application of ryanodine (10(-5) M). The caffeine-activated single-channel currents disappeared when 10 mM EGTA were added to the pipette solution or after replacement of external Ca2+ with Ba2+. These results show that these channels are Ca(2+)-dependent. Alteration of the Cl- equilibrium potential did not produce any change in the reversal potential of the caffeine-activated single-channel current, indicating that it was not carried by Cl- ions. The value of the reversal potential was about + 10 mV, irrespective of the CsCl-, KCl- or NaCl-containing solutions used to fill the pipette. Caffeine activated single-channel currents when cells were bathed in 90 mM Ba2+ plus 1 mM Ca(2+)- or 91 mM Ca(2+)-containing solutions, showing that divalent cations permeate the channels.(ABSTRACT TRUNCATED AT 250 WORDS)
游离胞质Ca2+浓度的快速短暂升高是平滑肌细胞激活最早出现的事件之一，并参与了几类Ca2+敏感离子通道（如K+通道和Cl-通道）的开放。在门静脉平滑肌细胞中，除了Ca(2+)依赖性Cl电流外，在移液管溶液中不存在EGTA的情况下，对外加10 mM咖啡因可记录到单通道活性。对于膜电位在-100至+60 mV之间变化的情况，这种新型通道的电导约为200 pS。单通道活性也可由外加去甲肾上腺素（10(-5) M）或乙酰胆碱（10(-5) M）、通过电压依赖性Ca(2+)通道的Ca2+内流以及细胞内应用ryanodine（10(-5) M）诱导产生。当向移液管溶液中加入10 mM EGTA或用Ba2+替代细胞外Ca2+后，咖啡因激活的单通道电流消失。这些结果表明这些通道是Ca(2+)依赖性的。改变Cl-平衡电位对咖啡因激活的单通道电流的反转电位没有产生任何影响，表明该电流不是由Cl-离子携带的。反转电位的值约为+10 mV，与用于填充移液管的含CsCl-、KCl-或NaCl的溶液无关。当细胞浸浴在90 mM Ba2+加1 mM Ca(2+)或91 mM Ca(2+)的溶液中时，咖啡因可激活单通道电流，表明二价阳离子可通透这些通道。（摘要截短于250字）
