Inhibitors of Ca2+ release from the isolated sarcoplasmic reticulum. I. Ca2+ channel blockers

The effects of Ruthenium red and tetracaine, which inhibit Ca2+-induced Ca2+ release from the isolated sarcoplasmic reticulum (e.g., Ohnishi, S.T. (1979) J. Biochem. (Tokyo) 86, 1147-1150), on several types of Ca2+ release in vitro were investigated. Ca2+ release was triggered by several methods: (1) addition of quercetin or caffeine, (2) Ca2+ jump, and (3) replacement of potassium gluconate with choline chloride to produce membrane depolarization. The time-course of Ca2+ release was monitored using stopped-flow spectrophotometry and arsenazo III as a Ca2+ indicator. Ruthenium red inhibited all of these types of Ca2+ release with the same concentration for half-inhibition C1/2 = 0.08-0.10 microM. Similarly, tetracaine inhibited these types of Ca2+ release with C1/2 = 0.07-0.11 mM. Procaine also inhibits both types of Ca2+ release induced by method 2 and 3 with C1/2 = 0.67-1.00 mM. These results suggest that Ruthenium red, tetracaine and procaine interfere with a common mechanism of the different types of Ca2+ release. On the basis of several pieces of evidence we propose that Ruthenium red and tetracaine block the Ca2+ channel of sarcoplasmic reticulum.