Modulation of stimulus-secretion coupling in single rat gonadotrophs

Paul Thomas, Dennis W. Waring

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1. Exocytosis and intracellular [Ca2+] were determined simultaneously in single anterior pituitary gonadotrophs from ovariectomized female rats. Dispersed cells were cultured for 2–4 days with or without 0.2 nm oestradiol‐17 β (E2) before use. Cells were stimulated with either gonadotrophin releasing hormone (GnRH) or by membrane depolarization. Exocytosis was determined from the change in membrane capacitance (Cm) using the perforated‐patch whole‐cell recording technique. Intracellular [Ca2+] was measured using fura‐2 fluorescence.

2. The exocytotic response to 1 nm GnRH was characterized by a wide spectrum of responses, ranging from exocytotic bursts to relatively slow, graded increases that were dependent on the evoked intracellular Ca2+ pattern. A kinetic model is presented that incorporates the observed steep dependence of exocytosis on measured intracellular [Ca2+]; simulated exocytosis reasonably approximated observed exocytotic responses, both kinetically and quantitatively. The model also suggests that the modulatory effects of E2 are brought about either by a change in the Ca2+ sensitivity of exocytosis or by a preferential clustering of docked‐secretory granules close to sites of Ca2+ release. The results suggest that in gonadotrophs an oscillatory Ca2+ signal is sensed by the exocytotic apparatus in a modified form of digital encoding.

3. Exocytosis in E2‐treated cells was 3‐fold greater than in non‐treated cells for GnRH‐evoked secretion, and 38% greater for depolarization; however, there was no effect of E2 on the intracellular Ca2+ response to either stimulus. The results show that maximum expression of the effect of E2 on exocytosis requires activation of GnRH‐dependent pathways.
Original languageEnglish
Pages (from-to)705-719
Number of pages15
JournalThe Journal of Physiology
Issue number3
Publication statusPublished - Nov 1997

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