The modulation and characterisation of the Ca2+‐induced Ca2+ release mechanism in cultured human myometrial smooth muscle cells

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Abstract
The process of Ca2+‐induced Ca2+ release (CICR) was studied in saponin permeabilised human myometrial smooth muscle cells in which the sarcoplasmic reticulum (SR) was pre‐loaded with 45Ca2+. A rise in the free Ca2+ concentration of the bathing solution from 100 nM tot 10 μM increased the rate of 45Ca2+ loss, while a reduction to 10 nM decreased the rate of 45Ca2+ loss. Ruthenium red (20 μM) lowered the basal rate of 45Ca2+ loss and reduced CICR. Caffeine did not activate 45Ca2+ release although ryanodine induced 45Ca2+ release and CICR was augmented in the presence of caffeine. These data suggest the operation of a Ca2+‐activated 45Ca2+ release process which is similar in many of its properties to the CICR process described in many cells. The basic properties of the CICR mechanism in myometrium differs in many respects from the CICR process recently described in human vascular smooth muscle.