Fig. 6.

TCS concomitantly affects both RyR and DHPR activity without depleting SR Ca²⁺ stores. (A) Mouse skeletal myotubes were loaded with the Ca²⁺ indicator Fluo-4 and electrically stimulated. Perfusion with 10 μM TCS resulted in a profound change in resting Ca²⁺, as well as a rapid diminution and abrogation of Ca²⁺ transients. Challenge with 20 mM caffeine (Caff) indicates SR Ca²⁺ stores were not depleted. (Inset) In separate experiments, after TCS caused failure of myotubes to respond to electrical stimuli, challenge with 60 mM KCl (K⁺) also failed to elicit ECC. (B) Dyspedic myotubes lacking RyR1 exhibited little change in cytosolic Ca²⁺ when exposed to TCS, implicating RyR1 as a molecular target of TCS. (C) Mouse skeletal muscle preparations were incubated with [³H]ryanodine or [³H]PN200 in the presence of TCS. TCS increased specific [³H]ryanodine binding with respect to control, whereas specific [³H]PN200 binding was inhibited noncompetitively across similar TCS concentrations.