Altura B T, Zhang A M, Altura B M
Department of Physiology, State University of New York, Brooklyn.
Magnes Trace Elem. 1990;9(3):163-75.
Small reductions in external sodium ions [( Na+]o), which cause no contractile effects in normal Mg2(+)-containing medium, cause an immediate contraction when [Mg2+]o is simultaneously withdrawn from isolated rat aortic smooth muscle. These contractions are Ca2(+)-dependent and vary in magnitude with the extracellular Na concentration and the Na substitute used. In contrast to substitution with sucrose, mannitol, urea and choline, substitution with Tris or Li+ does not result in contractions, in the absence of [Mg2+]o with these comparatively low [Na+]o reductions. Choline, mannitol, sucrose and urea substitutions sometimes give rise to a fast contractile phase in the presence of [Mg2+]o, which relaxes within a short time (about 5 min). The rises in tension in response to lowering of [Na+]o in the absence of [Mg2+]o are inhibited by the Na+ influx blocker, amiloride. These data are compatible with the hypothesis that Mg2+ controls Na+/Ca2+ exchange in these low Na+ substitution experiments and also protects the cell from osmotically induced small changes in cell volume in rat aortic smooth muscle.
在含正常镁离子（[Mg2+]o）的培养基中，外部钠离子浓度（[Na+]o）的小幅降低不会引起收缩效应，但当从离体大鼠主动脉平滑肌中同时去除[Mg2+]o时，会立即引发收缩。这些收缩依赖于钙离子（Ca2+），其幅度会因细胞外钠浓度和所使用的钠替代物而有所不同。与用蔗糖、甘露醇、尿素和胆碱进行替代不同，在用Tris或Li+进行替代时，在没有[Mg2+]o且[Na+]o相对小幅降低的情况下，不会引发收缩。在有[Mg2+]o存在时，胆碱、甘露醇、蔗糖和尿素替代有时会引发一个快速收缩期，该收缩期会在短时间内（约5分钟）松弛。在没有[Mg2+]o时，因[Na+]o降低而引起的张力升高会被钠离子内流阻滞剂氨氯地平所抑制。这些数据与以下假设相符：在这些低钠替代实验中，镁离子控制着钠/钙交换，并且还保护细胞免受大鼠主动脉平滑肌中渗透压诱导的细胞体积微小变化的影响。
