Kentish J C, Jewell B R
J Gen Physiol. 1984 Jul;84(1):83-99. doi: 10.1085/jgp.84.1.83.
McClellan and Winegrad (1980, J. Gen. Physiol., 75:283-295) have reported that in rat ventricular muscles that have reportedly been made "hyperpermeable" to small ions such as Ca2+, CaEGTA2-, and MgATP2- by a soak in EGTA, the maximum Ca2+-regulated force can be permanently increased by a short exposure to positively inotropic drugs, such as epinephrine or cAMP plus theophylline, in the presence of the detergent Triton X-100. The experiments reported here were begun as an attempt to repeat and extend this important observation. However, no evidence could be found for a potentiation of force that was not merely produced by Triton alone. In addition, the thickest muscles used (250-440 microns diameter) exhibited very low values for force per unit cross-sectional area, which suggested that either Ca2+ reached only a fraction of the myofibrils or the myofibrils were in a state of low contractility. The results of further experiments that were designed to test the permeability characteristics of these EGTA-treated muscles indicated that the movement of certain ions into these preparations was restricted, even in thin muscles (80-200 microns diameter). The rate of development of Ca2+-regulated force was slow (t1/2 approximately equal to 1-3 min), but was greatly accelerated after the muscles had been superfused with Triton X-100 (t1/2 approximately equal to 10-20 s). Removal of creatine phosphate (CP) in the presence of MgATP produced a partial rigor contracture in the EGTA-treated muscles. The results were consistent with the suggestion that the EGTA-treated muscles were permeable to some extent to Ca2+ and HCP2- ions but not to CaEGTA2- and MgATP2-. Thus, it would seem unlikely that the [Ca2+], [MgATP2-], and [Mg2+] in the immediate vicinity of the myofibrils in these preparations can be adequately controlled by the solution bathing the muscles.
麦克莱伦和瓦因格拉德（1980年，《普通生理学杂志》，75:283 - 295）报告称，在据报道通过在乙二醇双（β-氨基乙基醚）四乙酸（EGTA）中浸泡而对诸如钙离子（Ca²⁺）、乙二醇双（β-氨基乙基醚）四乙酸钙络合物（CaEGTA²⁻）和三磷酸镁腺苷（MgATP²⁻）等小离子“高通透”的大鼠心室肌中，在去污剂曲拉通X - 100存在的情况下，通过短暂暴露于正性肌力药物如肾上腺素或环磷酸腺苷（cAMP）加茶碱，最大钙离子调节力可被永久性增强。此处报告的实验最初旨在重复并扩展这一重要观察结果。然而，未发现并非仅由曲拉通单独产生的力增强的证据。此外，所使用的最粗的肌肉（直径250 - 440微米）每单位横截面积的力值非常低，这表明要么钙离子仅到达了肌原纤维的一部分，要么肌原纤维处于低收缩性状态。旨在测试这些经EGTA处理的肌肉的通透性特征的进一步实验结果表明，即使在细肌肉（直径80 - 200微米）中，某些离子进入这些标本的运动也受到限制。钙离子调节力的发展速率缓慢（半衰期约为1 - 3分钟），但在肌肉用曲拉通X - 100灌注后大大加快（半衰期约为10 - 20秒）。在三磷酸镁腺苷存在的情况下去除磷酸肌酸（CP）会在经EGTA处理的肌肉中产生部分强直收缩。这些结果与经EGTA处理的肌肉在一定程度上对钙离子和磷酸肌酸离子（HCP²⁻）通透但对乙二醇双（β-氨基乙基醚）四乙酸钙络合物和三磷酸镁腺苷不通透的推测一致。因此，这些标本中肌原纤维紧邻区域的钙离子、三磷酸镁腺苷和镁离子浓度似乎不太可能通过浸泡肌肉的溶液得到充分控制。
