Cyclic Ca2+Changes in Intracellular Stores of Gonadotropes During Gonadotropin-Releasing Hormone-Stimulated Ca2+Oscillations

Gonadotropin-releasing hormone induces oscillatory release of Ca2+from inositol trisphosphate-sensitive stores of gonadotropes. Simultaneously with electrophysiological measures of cytoplasmic [Ca2+], corresponding changes in [Ca2+] within intracellular stores were monitored with a fluorescent dye, mag-indo-1. Each cycle of oscillation released only 10% of the detectable stored Ca2+. Some Ca2+was recovered by the stores using a mechanism sensitive to inhibitors of intracellular Ca2+ATPases, 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 and refilling of a single compartment. The free concentrations measured show that intracellular Ca2+store compartments contain strong Ca2+buffers.