Figure 6. Ca²⁺ efflux associated with PCr withdrawal is insensitive to ryanodine or Ruthenium Red.

A, after three caffeine-induced Ca²⁺transients, PCr was withdrawn, resulting in a slow prolonged release of Ca²⁺ from the SR. B, after 6 min, the [PCr] was increased again to 10 mM (not shown) and the steady-state caffeine-induced Ca²⁺ transients returned to near-control level. C, after treatment with 20 μm ryanodine for 10 min, the caffeine-induced Ca²⁺ transients were almost completely abolished. The Ca²⁺ release associated with PCr was essentially unaffected by ryanodine (D) or by further treatment with 50 μm Ruthenium Red (E). All responses were obtained in the same preparation.