Cytosolic free calcium levels in cultured pituitary cells separated by centrifugal elutriation: effect of gonadotropin-releasing hormone.

The cytosolic concentration of free Ca 2+ ((Ca' 2+ )i) in normal rat pituitary cells separated by centrifugal elutriation was monitored with the fluorescent Ca 2+ indicator Quin 2. GnRH (10~ 7 M) induced a rapid rise (6-8 sec) in the gonadotroph's (Ca 2+ )i, followed by a plateau phase of prolonged elevated (Ca 2+ )i which lasted about 15 min. The stimulatory effect of GnRH was dose dependent, with an ED50 of 10~ 9 M, and was blocked by the potent antagonist (Dp- Glu'.pclPhe'.DTrp^lGnRH. GnRH elevated (Ca 2+ )iOnly in go- nadotroph-enriched cell fractions, whereas TRH and GH-re- leasing factor (GRF) elevated (Ca 2+ )j in mammotroph- and so- matotroph-enriched cells fractions, respectively. A rapid in- crease (first phase) in (Ca 2+ )j induced by GnRH was observed in Ca 2+ -free medium containing EGTA, but this rapid phase was terminated within 2 min. Readdition of Ca