Ca 2+ -Stimulated Respiration in Mitochondria Isolated From Different Fiber Types of Normal Chick Muscle and From Dystrophic Muscle 1

Abstract

Summary

Mitochondria were isolated from normal chick muscles composed predominantly of αW, αR, or βR fibers and compared polarographically. Rates of respiration after addition of ADP were higher for mitochondria from αR and βR fibers than for mitochondria from αW fibers. Respiration of mitochondria from all three fiber types was enhanced by the addition of Ca²⁺ to the medium but at rates similar to those observed after addition of ADP. Ca²⁺/O ratios were not different for the mitochondria from the different fiber types.

Mitochondria were isolated from the pectoralis muscle (αW) of normal chicks and chicks with hereditary muscular dystrophy. Mitochondria from dystrophic chick muscle exhibited higher rates of respiration after addition of ADP than mitochondria from normal chick muscle. Respiration in mitochondria from both genotypes was enhanced proportionately by the addition of Ca²⁺. Dystrophic organelles accumulated more Ca²⁺ than normal mitochondria during Ca²⁺-stimulated respiration, but the increased uptake was proportional to this higher rate of respiration. Freshly isolated mitochondria from dystrophic muscle contained higher levels of Ca²⁺ than those from normal muscle. Since very high levels of EDTA (10 mM) were used throughout the isolation procedure, it is suggested that dystrophic muscle mitochondria may have a higher binding capacity for Ca²⁺.