Intracellular free Mg2+concentration in skeletal muscle fibres of frog and crayfish

✍ Scribed by D. Günzel; S. Galler

• Publisher: Springer
• Year: 1991
• Tongue: English
• Weight: 975 KB
• Volume: 417
• Category: Article
• ISSN: 0031-6768
• DOI: 10.1007/bf00370938

✦ Synopsis

The free intracellular Mg z+ concentration ([Mg 2 +]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 retool/1 MgCI2, the mean [Mg2+]i of the frog muscle fibres was 1.3 retool/1. In phasic crayfish muscle fibres, [Mg 2 +]i was about twice as high (mean 3.5 retool/t) as in tonic fibres (mean 1.5 retool/l), measured in van Harreveld solution containing 1.2 retool/1 MgCI2. Long-lasting (3 -12 h) incubation of frog skeletal muscle fibres in Na +-free solution produced a reversible increase of [Mg 2 +]i by a factor of about 1.7. A tenfold rise of extracellular Mg 2 + led to an increase in [Mg 2 +]i in the presence as well as in the absence ofNa +. In these experiments, mean [Mg2+]i values of 3.2 mmol/1 were never exceeded. Thus, [Mg 2 +]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 Mg 2+ extrusion mechanism, which is regulated by actual Mg 2+ concentrations.