Lack of involvement of sarcoplasmic reticulum in myopathy of acute phosphorous depletion.

Acute and chronic hypophosphatemia are known to cause metabolic myopathy. It has been proposed that impaired Ca transport in subcellular membranes is involved in its genesis. In the present study, calcium transport in the sarcoplasmic reticulum (SR), concentrations of ions or nucleotides and transmembrane potential were investigated in muscles of acutely hypophosphatemic rats, i.e. animals with chronic dietary phosphorous deprivation (PD) and superimposed acute hypophosphatemia resulting from the administration of insulin and glucose. Despite hypophosphatemia and low muscle phosphorous concentration, no significant change of the initial rate of Ca uptake or Ca concentrating ability was observed in the SR of PD rats. Storing capacity was decreased; this may result from altered vesicle geometry. Water content, Na concentration, the concentration of several nucleotides and transmembrane potential of muscle were unchanged in PD rats. The findings document that no intrinsic abnormality of vectorial Ca transport is present in the SR of acutely hypophosphatemic PD animals.