Barium currents in developing skeletal muscle cells of normal and mutant mice foetuses with 'muscular dysgenesis'

The ontogenesis of Ca channel activities was studied in the developing myotubes of normal mice and mutant mice foetuses with 'Muscular Dysgenesis'. The ionic current through Ca channels was measured with Ba2+ as charge carrier using the whole cell clamp technique. All dissociated myotubes from foetuses (14th to 18th day of gestation) showed two distinct inward Ba currents: a low threshold, transient current (T-type) and a high threshold sustained current. In normal myotubes, T-type current density increased from the 14th day to the 16th day of gestation. After day 16, T-type current density decreased gradually until birth. Similar changes in T-type current density were observed in developing dysgenic myotubes where the current density was about 40% of that measured in normal myotubes throughout the prenatal period studied. The high threshold sustained current (L-type current) density increased gradually with age in normal myotubes while absent in dysgenic muscle. The latter, regardless of age, showed a high threshold current (Idys) which is distinct from the L-type current. Idys density did not change during the prenatal myogenesis period studied.