Wang Q, Akbarali H I, Hatakeyama N, Goyal R K
Center for Swallowing and Motility Disorders, Beth Israel Hospital, Harvard Medical School, Boston 02215, USA.
Am J Physiol. 1996 Nov;271(5 Pt 1):C1725-34. doi: 10.1152/ajpcell.1996.271.5.C1725.
Cl- and cation currents may play important roles in esophageal smooth muscle membrane potential changes and contraction. We studied Ca2+ release-activated cell-shortening and membrane currents in single cells freshly dispersed from the circular muscle of the opossum esophagus using the standard patch-clamp whole cell recording method. Caffeine (10-20 microM) and carbachol (10-100 microM) shortened the single smooth muscle cells by releasing intracellular Ca2+. At a holding potential of 0 mV, spontaneous transient outward currents STOCs, representing spontaneous Ca(2+)-activated K+ currents) were recorded. Caffeine, carbachol, or ionomycin evoked large outward currents (up to 1,650 pA) and subsequently abolished STOCs. At a holding potential of -50 mV in K(+)-containing solutions, an outward current in response to the agonists was observed; in some cells, the outward current followed an inward current. In K(+)-free solutions, the agonists induced only an inward current whose reversal potential was shifted by alteration of the anion gradient but not by that of the cation. With a low-Cl- pipette solution (Cl- substituted by glucuronate or glutamate), the inward currents were dependent mainly on the external cation gradient. This cation channel was permeable to Ba2+. Inclusion of 10 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid in the pipette solution abolished all these currents. These data suggest that in the opossum esophageal circular muscle 1) Ca2+ released from the intracellular stores by caffeine and carbachol is sufficient to induce single smooth muscle cell contraction and 2) the caffeine-, carbachol-, and ionomycin-induced membrane currents consist of Ca(2+)-activated K+, Cl-, and cation conductances.
氯离子和阳离子电流可能在食管平滑肌膜电位变化和收缩过程中发挥重要作用。我们使用标准膜片钳全细胞记录方法，研究了从负鼠食管环行肌中新鲜分离的单个细胞中的钙释放激活的细胞缩短和膜电流。咖啡因（10 - 20微摩尔）和卡巴胆碱（10 - 100微摩尔）通过释放细胞内钙离子使单个平滑肌细胞缩短。在0 mV的钳制电位下，记录到了代表自发钙激活钾电流的自发瞬时外向电流（STOCs）。咖啡因、卡巴胆碱或离子霉素诱发了大的外向电流（高达1650皮安），随后消除了STOCs。在含钾溶液中-50 mV的钳制电位下，观察到了对激动剂的外向电流；在一些细胞中，外向电流跟随内向电流。在无钾溶液中，激动剂仅诱导出一种内向电流，其反转电位因阴离子梯度的改变而发生偏移，但不受阳离子梯度改变的影响。使用低氯移液管溶液（用葡萄糖醛酸或谷氨酸替代氯离子）时，内向电流主要依赖于外部阳离子梯度。这种阳离子通道对钡离子通透。移液管溶液中加入10 mM乙二醇双（β-氨基乙基醚）-N，N，N'，N'-四乙酸消除了所有这些电流。这些数据表明，在负鼠食管环行肌中：1）咖啡因和卡巴胆碱从细胞内储存释放的钙离子足以诱导单个平滑肌细胞收缩；2）咖啡因、卡巴胆碱和离子霉素诱导的膜电流由钙激活钾、氯和阳离子电导组成。
