Sarcoplasmic reticulum in aged skeletal muscle.
A decrease in muscle mass and strength and a slowing of muscle contraction are common features of the ageing process. Recent advances in basic biochemical knowledge have provided new insights into pathogenetic mechanisms underlying age-related changes in the excitation-contraction coupling process, Ca2+-transients and isometric twitch-contraction time. Sarcoplasmic reticulum (SR) Ca2+-pumps are not basically altered in physiological ageing, but several aspects of the Ca2+-transport system remain controversial, regarding phosphorylation-dependent regulation in slow-twitch muscles, in particular. It seems that conflicting reports and divergent interpretations concerning the effect of ageing on SR Ca2+-release arise from the type of muscle, the stage of the ageing process and the animal species. A cause-effect relationship between the decrease in dihydropyridine receptors and in muscle strength is strongly suggested by studies in transgenic mice, but is unsupported by our studies with fast-twitch and slow-twitch muscles of old rats. Our experimental evidence also seems to exclude the occurrence of age-related changes in the number and in the functional behaviour of Ca2+-release channels/ryanodine receptors (RyR1), based on ¿3H-ryanodine binding studies. There is emerging, although only suggestive evidence, so far, that modulation of RyR1 by SR luminal protein calsequestrin, or the functional coupling of RyRs by FKBP-12, may be altered in ageing skeletal muscle.
Margreth
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A
NRC Unit for Muscle Biology and Physiopathology, Department of Experimental Biomedical Sciences, University of Padova, viale G. Colombo, Padova, Italy.
Damiani
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E
Bortoloso
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E
D000375:Aging / Q000378:metabolism* / Q000502:physiology; D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D006801:Humans; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000502:physiology; D051381:Rats; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*
D000252:Calcium-Transporting ATPases; D002118:Calcium