Figure 2.

Homozygous and heterozygous expression of I4897T in dyspedic myotubes does not alter luminal SR Ca²⁺ levels monitored with Fluo-3. (A) CPA-induced Ca²⁺ transients in intact, fluo-3 AM-loaded dyspedic myotubes expressing RyR1 alone (Left), RyR1/I4897T (Center), or I4897T alone (Right). (B) Average maximal values of slow CPA-induced Ca²⁺ transients obtained from intact myotubes (mean ± SEM). Control experiments revealed that 30 μM CPA induced a similar fluorescence increase in intact normal (0.98 ± 0.30, n = 7) and dyspedic (1.07 ± 0.20, n = 7) myotubes. These values were not significantly different from those of RyR1-, I4897T-, or RyR1/I4897T-expressing myotubes (P > 0.3). In addition, RyR1- and I4897T-expressing myotubes exhibited CPA-induced Ca²⁺ transients of similar magnitude even when elicited in a nominally Ca²⁺-free external solution. (C) CPA-induced Ca²⁺ transients measured in whole-cell patch clamped dyspedic myotubes expressing RyR1 alone (Left), RyR1/I4897T (Center), or I4897T alone (Right). (D) Average maximal values of CPA-induced Ca²⁺ transients obtained from C (mean ± SEM).