Figure 5. MCa fails to induce Ca²⁺ release from cardiac HSR vesicles.

Representative traces of extravesicular Ca²⁺ concentration variations measured using Antipyrylazo III, a Ca²⁺ indicator. Skeletal HSR vesicles (A) and cardiac HSR vesicles (B) were actively loaded with Ca²⁺ by sequential addition of 20 μM CaCl₂ (final concentration) in the cuvette. After each Ca²⁺ addition, the absorbance was monitored until the initial baseline value was reached. MCa-induced Ca²⁺ release was then tested on skeletal and cardiac HSR vesicles by addition of 25 nM MCa to skeletal HSR (A) and 1 μM MCa to cardiac HSR (B). Integrity of the cardiac vesicles and functionality of the RyR2 channel were assessed by injection of 1.5 mM thymol, 10 min after the application of MCa.