Pollock N S, Kargacin M E, Kargacin G J
Department of Physiology and Biophysics, University of Calgary, Calgary, Alberta T2N 4N1, Canada.
Biophys J. 1998 Oct;75(4):1759-66. doi: 10.1016/S0006-3495(98)77617-9.
Despite the fact that Ca2+ transport into the sarcoplasmic reticulum (SR) of muscle cells is electrogenic, a potential difference is not maintained across the SR membrane. To achieve electroneutrality, compensatory charge movement must occur during Ca2+ uptake. To examine the role of Cl- in this charge movement in smooth muscle cells, Ca2+ transport into the SR of saponin-permeabilized smooth muscle cells was measured in the presence of various Cl- channel blockers or when I-, Br-, or SO42- was substituted for Cl-. Calcium uptake was inhibited in a dose-dependent manner by 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB) and by indanyloxyacetic acid 94 (R(+)-IAA-94), but not by niflumic acid or 4,4'-dinitrostilbene-2,2'-disulfonic acid (DNDS). Smooth muscle SR Ca2+ uptake was also partially inhibited by the substitution of SO42- for Cl-, but not when Cl- was replaced by I- or Br-. Neither NPPB nor R(+)-IAA-94 inhibited Ca2+ uptake into cardiac muscle SR vesicles at concentrations that maximally inhibited uptake in smooth muscle cells. These results indicate that Cl- movement is important for charge compensation in smooth muscle cells and that the Cl- channel or channels involved are different in smooth and cardiac muscle cells.
尽管钙离子转运到肌肉细胞的肌浆网（SR）中是生电的，但SR膜上并未维持电位差。为了实现电中性，在钙离子摄取过程中必须发生补偿性电荷移动。为了研究氯离子在平滑肌细胞这种电荷移动中的作用，在存在各种氯离子通道阻滞剂的情况下，或者用碘离子、溴离子或硫酸根离子替代氯离子时，测量了皂素通透的平滑肌细胞中钙离子向SR的转运。5-硝基-2-（3-苯丙基氨基）苯甲酸（NPPB）和茚满氧基乙酸94（R（+）-IAA-94）以剂量依赖的方式抑制钙离子摄取，但氟尼辛或4,4'-二硝基芪-2,2'-二磺酸（DNDS）则无此作用。用硫酸根离子替代氯离子也会部分抑制平滑肌SR的钙离子摄取，但用碘离子或溴离子替代氯离子时则不会。在最大程度抑制平滑肌细胞摄取的浓度下，NPPB和R（+）-IAA-94均未抑制钙离子摄取到心肌SR囊泡中。这些结果表明，氯离子移动对平滑肌细胞的电荷补偿很重要，并且平滑肌和心肌细胞中涉及的氯离子通道不同。
