THE MODULATION AND CHARACTERIZATION OF THE CA2+-INDUCED CA2+ RELEASE MECHANISM IN CULTURED HUMAN MYOMETRIAL SMOOTH-MUSCLE CELLS

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 Ca-45(2+). A rise in the free Ca2+ concentration of the bathing solution from 100 nM tot 10 mu M increased the rate of Ca-45(2+) loss, while a reduction to 10 nM decreased the rate of Ca-45(2+) loss. Ruthenium red (20 mu M) lowered the basal rate of Ca-45(2+) loss and reduced CICR. Caffeine did not activate Ca-45(2+) release although ryanodine induced Ca-45(2+) release and CICR was augmented in the presence of caffeine. These data suggest the operation of a Ca2+-activated Ca-45(2+) 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.