Intracellular Mg2+ diffusion within isolated rat skeletal muscle fibers.
Intracellular free magnesium concentration ([Mg2+]i) was measured in enzymatically isolated rat skeletal muscle fibers using the fluorescent dye mag-indo-1. The change in [Mg2+]i produced by a local intracellular microinjection of magnesium pidolate (magnesium pyrrolidone carboxylate) was measured at a given distance from the injection site. In one series of experiments this protocol was tested on isolated fibers that were completely embedded into silicone grease: under these conditions, the injection produced an increase in [Mg2+]i that reached a steady level some time following the injection. The time-course of the [Mg2+]i change could be well accounted for by a model of longitudinal diffusion. The mean apparent Mg2+ diffusion coefficient (D(app)) was 188+/-9 microm2 s(-1) (n = 16), approximately four times lower than the value measured in vitro. This reduction likely results from the effects of cytoplasmic viscosity and of Mg2+ binding to low affinity static sites. Another series of measurements was performed on fibers that were either partially or completely free of silicone: under these conditions, the time course of the change in [Mg2+]i was in many cases more complex than predicted by simple diffusion.
Bernengo
J C
JC
Centre Commun de Quantimétrie, Université Claude Bernard Lyon 1, France.
Collet
C
C
Jacquemond
V
V
D000818:Animals; D004058:Diffusion; D066298:In Vitro Techniques; D008274:Magnesium / Q000378:metabolism*; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
D008274:Magnesium