Ruthenium red selectively prevents Ins(1,4,5)P3-but not caffeine-gated calcium release in avian atrium

We previously reported that inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] and caffeine evoked contractures in saponin-permeabilized chick atria. The magnitude of contractures evoked by maximally effective concentrations of Ins(1,4,5)P3 were half those evoked by maximally effective concentrations of caffeine. In the present report, we tested the hypothesis that these two agents may act on distinct calcium-release mechanisms by comparing the effects of ryanodine, ruthenium red, and procaine on the responses to Ins(1,4,5)P3 and caffeine. We find that procaine inhibits both responses with similar mean inhibitory concentrations in the millimolar range. Nanomolar concentrations of ryanodine selectively potentiate the contractures induced by Ins(1,4,5)P3 but have no effect on those induced by caffeine. Micromolar concentrations of ryanodine inhibit responses to both Ins(1,4,5)P3 and caffeine in a use-dependent way. Ruthenium red prevents the response to Ins(1,4,5)P3 and potentiates that to caffeine, as if rutheniu...