A novel ryanodine sensitive calcium release mechanism in cultured human myometrial smooth‐muscle cells

Abstract

In cultured human myometrial cells application of caffeine (1–30 mM) did not result in an elevation of intracellular Ca²⁺ ([Ca²⁺]_i). Caffeine was found to reversibly inhibit both spontaneous and agonist-induced repetitive rises in [Ca²⁺]_i possibly as a consequence of its ability to interfere with the binding of inositol trisphosphate (IP₃) to the receptor on the sarcoplasmic reticulum. Brief applications of ryanodine (1–10μM) were observed to elevate [Ca²⁺]_i and repeated exposures to ryanodine could elicit Ca²⁺ transients of similar magnitude. Ryanodine was also observed to mobilise Ca²⁺ in cells bathed in nominally Ca²⁺-free solution. These observations suggest the presence of a novel type of ryanodine-sensitive Ca²⁺-induced Ca²⁺ release (R-CICR) system in human myometrial cells.