Ca2+ binding, ATP-dependent Ca2+ transport, and total tissue Ca2+ in embryonic and adult avian dystrophic pectoralis

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Abstract
Avian muscular dystrophy is an autosomal recessive genetic disease characterized by early hypertrophy and loss of function of the pectoralis major. The disease is progressive, ultimately resulting in atrophy and heavy lipid deposition. Previous investigators have noted a decrease in the ability of the dystrophic sarcoplasmic reticulum to concentrate Ca2+. More recently, other investigators have shown an abnormal calcium uptake in avian dystrophic sarcoplasmic reticulum. They indicated, using freeze-fracture techniques, that a 90 Å particle of the vesicle membrane exhibited a decreased population and suggested that they might be the ATPase involved in calcium transport. Our studies confirm the earlier observations of a decreased rate of Ca2+ uptake and Ca2+ binding capacity of dystrophic fragmented sarcoplasmic reticulum vesicles which are isolated from both embryonic and adult pectoralis. These observations correlate in turn with a 75% drop in the Ca: ATP transport efficiency of the dystrophic sarcoplasmic reticulum determined by measuring the rate of32Pi liberation from γ-ATP32 during active calcium transport by the isolated sarcoplasmic reticulum SR. In addition, we have found a quantitative deficiency in a 65,000 dalton component of the dystrophic fragmented SR at the time of myoblast fusion by measuring35S-Methionine incorporation into the SR, coupled to high resolution polyacrylamide gel electrophoresis and radioautography. Analysis of total tissue calcium by atomic absorption spectroscopy revealed a decrease in the total calcium content of dystrophic muscle.