MODULATION BY PREDNISOLONE OF CALCIUM HANDLING IN SKELETAL-MUSCLE CELLS

1 Increased calcium (Ca2+) influx has been incriminated as a potential pathological mechanism in the chronic skeletal muscle degeneration exhibited by Duchenne muscular dystrophy (DMD) patients. We have studied the influence of the glucocorticoid alpha-methylprednisolone (PDN), the only drug known to have a beneficial effect on the degenerative course of DMD, on Ca2+ handling in the C2 skeletal muscle cell line. 2 PDN, when added 3 days (when myoblasts start to fuse into myotubes) after cell seeding, led to a 2 to 4 fold decrease in cellular Ca2+ uptake. This decrease was independent of the extracellular Ca2+ concentration applied to cells. The effect took at least 24 h in order to become established (PDN of 10(-5) M) and took longer for lower PDN concentrations (EC(50) of ca. 10(-6) M at day 5, 10(-6.5) M at day 7 and 10(-7.5) M at day 9 in culture). 3 Cellular calcium accumulation was also decreased in PDN-treated myotubes exposed to Ca-45(2+)- containing medium for 1 to 6 days. 4 No effect of PDN was seen on Ca-45(2+) efflux; a decrease in the amount of Ca-45(2+) released was observed due to the reduction of cellular Ca-45(2+) loading. 5 PDN treatment led to an approximately 2 fold decrease in basal cytosolic Ca2+ concentration. 6 Three antioxidant drugs (lazaroids), previously shown to enhance in vitro skeletal muscle cell differentiation to the same extent as PDN, induced a similar decrease in Ca2+ influx. 7 Our results suggest that long-term incubation of C2 cells with PDN leads to a decrease of the size of the cellular Ca2+ pools and to reduced resting cytosolic Ca2+ levels. Part of the beneficial effect of PDN in DMD patients could be attributed to a reduction of Ca2+ influx and of the size of Ca2+ pools in dystrophic muscle fibres.