Tubular aggregates: Sarcoplasmic reticulum origin, calcium storage ability, and functional implications

Muscle biopsy specimens from three patients with an autosomal dominant myopathy and tubular aggregates in both type 1 and type 2 fibers16 were investigated for immunofluorescent staining with antibodies to sarcoplasmic reticulum (SR) Ca‐pump protein and calsequestrin and for Ca2+ loading ability. The results show that type 1 and type 2 fibers are differentially reactive to anti–ca‐pump protein lgG and similarly reactive with affinity‐purified antibody to calsequestrin, which is in agreement with earlier observations in rat skeletal muscle.8 Tubular aggregates, which are shown to be highly reactive with either kind of antibody, appear to be sites of calcium accumulation for oxalatefacilitated adenosine triphosphate (ATP) dependent Ca uptake by chemically skinned fibers and thereby increase markedly the Ca loading capacity of the affected fibers.