Postnatal development of Ca2+-sequestration by the sarcoplasmic reticulum of fast and slow muscles in normal and dystrophic mice.
Ca2+-uptake activities of the sarcoplasmic reticulum (SR) were determined with a Ca2+-sensitive electrode in homogenates from fast- and slow-twitch muscles from both normal and dystrophic mice (C57BL/6J strain) of different ages. Immunochemical quantification of tissue Ca2+-ATPase content allowed determination of the specific Ca2+-transport activity of the enzyme. In 3-week-old mice of the dystrophic strain specific Ca2+ transport was already significantly lower than in the normal strain. It progressively decreased with maturation and reached only 40-50% and 30-50% of the normal values in fast- and slow-twitch muscles of adult dystrophic animals, respectively. Tissue contents of calsequestrin were reduced in both types of muscle leading to an increased Ca2+-ATPase to calsequestrin protein ratio. Equal amounts of the Ca2+-ATPase protein (detected by Coomassie blue staining of polyacrylamide gels) were present in SR vesicles isolated by Ca2+-oxalate loading from adult normal and dystrophic fast-twitch muscles. However, the specific ATP-hydrolysing activity of the enzyme was approximately 50% lower in dystrophic than in normal SR. The reduced ATP-hydrolysing activity was correlated with decreased Ca2+-transport activity, phosphoprotein formation and fluorescein isothiocyanate labeling as determined in total microsomal and heavy SR fractions. Although the Ca2+ and ATP affinities of the enzyme were unaltered, its ATPase activity was reduced at all levels of ATP in the dystrophic SR. Taken together, these findings point to a markedly impaired function of the SR and an increase in the population of inactive SR Ca2+-ATPase molecules in murine muscular dystrophy.
Leberer
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E
Fakultät für Biologie, der Universität Konstanz, Federal Republic of Germany.
Härtner
K T
KT
Pette
D
D
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000375:Aging / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D001692:Biological Transport; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002155:Calsequestrin / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D051379:Mice; D008810:Mice, Inbred C57BL; D009137:Muscular Dystrophy, Animal / Q000201:enzymology / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000201:enzymology / Q000378:metabolism*
D002155:Calsequestrin; D000255:Adenosine Triphosphate; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D002118:Calcium