Determination of skeletal muscle calpain and calpastatin activities during maturation
Ou, B.R.; Forsberg, N.E.
American Journal of Physiology 261(6 Pt 1): E677-E683
1991
ISSN/ISBN: 0002-9513 PMID: 1767827 Document Number: 383035
Our objectives were to characterize events underlying changes in skeletal muscle calpain and calpastatin activities, using maturation as a model. Muscle samples were taken from rabbits of four ages (newborn and 1, 2, and 5 mo. old). Concentrations of RNA and protein and activities of calpains I and II and calpastatin were determined. Steady-state concentrations of mRNAs encoding calpain I, calpain II, calpastatin, .alpha.- and .beta.-tubulin, and .beta.-actin were determined using Northern blot analysis. Calpain and calpastatin activities decline markedly between birth and 1 mo of age and remained unchanged thereafter. Several factors accounted for the neonatal losses of calpains and calpastatin. First, muscle protein concentration increased between birth and 1 mo of age and diluted calpain and calpastatin specific activities. Second there was a marked reduction of muscle RNA concentration between birth and 1 mo of age, which indicates that protein synthetic capacity declined with age. Finally, calpastatin mRNA concentration declined between birth and 1 mo of age and further contributed to developmental losses of calpastatin activity. Calpain I mRNA concentration was unaffected by age, and although calpain II mRNA concentration declined with age, losses were not detected between birth and 1 mo; hence age-related changes in calpain I and II activities are not mediated at the mRNA level. The age-related reductions in calpain II and calpastatin mRNA concentrations resembled age-related changes in .alpha.- and .beta.-tubulin and .beta.-actin mRNA concentration. Hence developmental attenuation of calpain II and calpastatin gene expression is associated with housekeeping gene expression and does not arise from direct regulation of calpain II and calpastatin gene expression.