DMCA
Regulation by Magnesium of Intracellular Calcium Movement in Skinned Muscle Fibers
BibTeX
@MISC{Stephenson_regulationby,
author = {Elizabeth W. Stephenson and Richard J. Podolsky},
title = {Regulation by Magnesium of Intracellular Calcium Movement in Skinned Muscle Fibers},
year = {}
}
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Abstract
(SR) and myofilament space (MFS) was studied in skinned muscle fibers by using isometric force as an indicator of MFS Ca. In Ca-loaded fibers at 20°C, the large force spike induced by Ca in 1 mM Mg (5 mM ATP) was strongly inhibited in 3 mM Mg, and force development was extremely slow. After a brief Ca stimulus in 1 mM Mg, relaxation in Ca-free solution was significantly faster in 3 mM Mg. These changes were due to altered Ca movements, since the effect of 3 mM Mg on steady force in CaEGTA solutions was small. Changes in Mg alone induced force transients apparently due to altered Ca movement. In relaxed fibers, decreasing the Mg to 0.25 mM caused phasic force development. In contracting fibers in Ca solutions, increasing the Mg caused a large transient relaxation. The effects of increased Mg were antagonized by 0.5 mM Cd, an inhibitor of the SR Ca transport system. The results indicate that active Ca uptake by the SR in situ is stimulated by Mg, and that it can affect local MFS [Ca ++] in the presence of a substantial Ca source. These results provide evidence that an increased rate of Ca uptake in 3 mM Mg could account for inhibition of the large force spike associated with Ca-induced Ca release in skinned fibers.
Keyphrases
mm mg skinned muscle fiber intracellular calcium movement ca movement large force spike ca solution active ca uptake mm cd sr ca transport system increased rate ca-free solution relaxed fiber ca-loaded fiber increased mg large transient relaxation steady force caegta solution myofilament space phasic force development substantial ca source force transient isometric force local mf ca mf ca ca-induced ca release skinned fiber brief ca stimulus force development
