Regulation of cytosolic calcium in skeletal muscle cells of the mdx mouse under conditions of stress

Abstract

1 In Duchenne muscular dystrophy (DMD) dysregulation of cytosolic calcium appears to be involved in the degeneration of skeletal muscle fibres. Therefore, we have studied the regulation of the free cytosolic calcium concentration ([Ca2+]) under specific stress conditions in cultured myotubes isolated from the hind limbs of wild-type (C57BL10) and dystrophin-deficient mutant mdx mice. [Ca2+] [Ca2+]c when the cells were exposed to the hypo-osmotic buffer (100 mOsm).5 Incubation of the cell culture for 3-5 days from the onset of induction of myotube formation with the membrane permeable protease inhibitor, calpeptin (50 gM) abolished the rise in [Ca2+]c in mdx myotubes upon exposure to hypo-osmotic shock.6 Treatment of the cell culture for 3-5 days with ac-methylprednisolone (PDN, 10 guM) attenuated the rise in [Ca2+]c following hypo-osmotic stress for both normal and mdx myotubes by about 50%.7 The results described here suggest an increased permeability of mdx myotubes to Ca2+ under specific stress conditions. The ameliorating effect of PDN on [Ca2+]c could explain, at least partly, the beneficial effect of this drug on DMD patients.

Dexamethasone stimulates store-operated calcium entry and protein degradation in cultured L6 myotubes through a phospholipase A2-dependent mechanism

“…It should be noted that although the present and other studies (7,37,40,45) are consistent with SOCE in skeletal muscle cells, the influence of glucocorticoids on muscle calcium entry and concentrations has been examined only in a few previous studies, with apparently conflicting results (41,51,57,74). The present finding of increased calcium entry and concentrations in muscle cells treated with dexamethasone is consistent with a report by Vandebrouck et al (74).…”

“…Importantly, the effects of glucocorticoids on SOCE were not determined in the reports by Ruegg and coworkers (41,51,57). The reason(s) for the conflicting results is not apparent but may be related to species differences, human muscle cells being studied by Vandebrouck et al (74) and mouse myocytes being used by Ruegg and coworkers (41,51,57).…”

“…Apparently conflicting results with regard to the effects of glucocorticoids on muscle cell calcium homeostasis were reported in a series of papers by Ruegg and coworkers (41,51,57). In those studies, treatment with methylprednisolone of C2C12 myotubes or of cultured muscle cells isolated from the hindlimbs of wild-type or dystrophin-deficient mutant mdx mice resulted in reduced calcium uptake and cellular concentrations of calcium.…”

“…The influence of glucocorticoids on muscle calcium homeostasis, however, is not well understood. Previous reports concerning the effects of glucocorticoids on calcium entry and concentrations in myocytes provided contradictory results, with evidence of both increased (74) and reduced (41,51,57) influx and cytosolic concentrations of calcium in glucocorticoid-treated muscle cells.…”

Mitochondrial Calcium Oscillations in C2C12 Myotubes

“…There is some controversy about this Ca 2ϩ elevation (1,4). Some groups (5,6) showed that basal cytosolic Ca 2ϩ concentration ([Ca 2ϩ ] c ) 1 was higher in dystrophic skeletal muscle cells relative to controls, whereas other laboratories (7,8) found that [Ca 2ϩ ] c was only increased under stress. To elucidate this contention, the redistribution of Ca 2ϩ into intracellular organelles should be examined.…”