Abstract
The rate of protein degradation in adult skeletal muscle in vitro is markedly enhanced by treatments that increase intracellular Ca2+. Fetal diaphragm degrades protein at much lower rates than adult muscle, and is unaffected by ambient Ca2+. In order to further define regulation of proteolysis during development, tyrosine release from skeletal muscle, incubated in vitro, was used as an index of protein degradation.
Tyrosine release in fetal muscle is unaffected by Ca2+ concentration, the calcium ionophore A23187 or muscle depolarization produced by elevated extracellular K+. Proteolysis in fetal muscle is reduced 35-40% by inhibitors of thiol proteinases (leupeptin or Ep-475) in the absence of Ca2+. Inhibition of ATP-dependent proteolysis by NaF or DNP occurs in fetal muscle independent of Ca2+. Methylamine, an inhibitor of lysosomal proteolytic activity, impedes ionophore-induced proteolysis in adult muscle but has no effect on fetal muscle. Ca2+-facilitated proteolysis is enhanced by nutrient deprivation in adult but not fetal muscle. The activities of lysosomal enzymes (cathepsin B, galactosidase, glucosaminidase and acid phospatase) in muscle homogenates do not vary during development.
These results indicate that proteolysis in fetal muscle is independent of calcium. Thus, the overall rate of protein breakdown in fetal muscle remains unaffected by physiologic or pathologic states that alter intracellular Ca2+ concentration.
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Greenberg, R., Wogenrich, J. CALCIUM DOES NOT REGULATE PROTEIN DEGRADATION IN FETAL MUSCLE. Pediatr Res 21 (Suppl 4), 214 (1987). https://doi.org/10.1203/00006450-198704010-00289
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DOI: https://doi.org/10.1203/00006450-198704010-00289