Günzel D, Galler S
Fakultät für Biologie, Universität Konstanz, Federal Republic of Germany.
Pflugers Arch. 1991 Jan;417(5):446-53. doi: 10.1007/BF00370938.
The free intracellular Mg2+ concentration ([Mg2+]i) was investigated in frog sartorius and crayfish phasic and tonic skeletal muscle fibres, using a new Mg2(+)-sensitive microelectrode based on the ionophore ETH 5214 [Hu et al. (1989) Anal Chem 61:574-576]. In Ringer solution containing 0.5 mmol/l MgCl2, the mean [Mg2+]i of the frog muscle fibres was 1.3 mmol/l. In phasic crayfish muscle fibres, [Mg2+]i was about twice as high (mean 3.5 mmol/l) as in tonic fibres (mean 1.5 mmol/l), measured in van Harreveld solution containing 1.2 mmol/l MgCl2. Long-lasting (3-12 h) incubation of frog skeletal muscle fibres in Na(+)-free solution produced a reversible increase of [Mg2+]i by a factor of about 1.7. A tenfold rise of extracellular Mg2+ led to an increase in [Mg2+]i in the presence as well as in the absence of Na+. In these experiments, mean [Mg2+]i values of 3.2 mmol/l were never exceeded. Thus, [Mg2+]i remained at least 60 times lower than predicted from a passive distribution across the cell membrane. The results suggest the existence of a Na(+)-dependent and a Na(+)-independent Mg2+ extrusion mechanism, which is regulated by actual Mg2+ concentrations.
使用基于离子载体ETH 5214的新型Mg2 +敏感微电极[Hu等人（1989年）《分析化学》61:574 - 576]，对青蛙缝匠肌以及小龙虾的相性和紧张性骨骼肌纤维中的细胞内游离Mg2 +浓度（[Mg2 +]i）进行了研究。在含有0.5 mmol/L MgCl2的林格氏溶液中，青蛙肌肉纤维的平均[Mg2 +]i为1.3 mmol/L。在含有1.2 mmol/L MgCl2的范哈雷维尔德溶液中测量时，小龙虾相性肌肉纤维中的[Mg2 +]i约为紧张性纤维（平均1.5 mmol/L）中的两倍（平均3.5 mmol/L）。将青蛙骨骼肌纤维在无Na +溶液中进行长时间（3 - 12小时）孵育，会使[Mg2 +]i可逆性增加约1.7倍。细胞外Mg2 +浓度升高十倍会导致无论有无Na +时[Mg2 +]i均增加。在这些实验中，平均[Mg2 +]i值从未超过3.2 mmol/L。因此，[Mg2 +]i仍比根据跨细胞膜被动分布预测的值低至少60倍。结果表明存在一种依赖Na +和不依赖Na +的Mg2 +外排机制，该机制受实际Mg2 +浓度调节。
