CYCLIC CA2-RELEASING HORMONE-STIMULATED CA2+ OSCILLATIONS( CHANGES ININTRACELLULAR STORES OF GONADOTROPES DURING GONADOTROPIN)

Gonadotropin-releasing hormone induces oscillatory release of Ca2+ fro m inositol trisphosphate-sensitive stores of gonadotropes. Simultaneou sly with electrophysiological measures of cytoplasmic [Ca2+], correspo nding changes in [Ca2+] within intracellular stores were monitored wit h a fluorescent dye, mag-indo-1. Each cycle of oscillation released on ly 10% of the detectable stored Ca2+. Some Ca2+ was recovered by the s tores using a mechanism sensitive to inhibitors of intracellular Ca2ATPases, and much of the remainder was temporarily and rapidly pumped into other intracellular compartments or out of the cell. The dynamics of Ca2+ oscillations are thus more complex than a repeated emptying a nd refilling of a single compartment. The free concentrations measured show that intracellular Ca2+ store compartments contain strong Ca2+ b uffers.