Modulation of stimulus-secretion coupling in single rat gonadotrophs

Area of Science:

• Endocrinology
• Cell Biology
• Neuroendocrinology

Background:

• Anterior pituitary gonadotrophs regulate reproductive functions.
• Exocytosis, the process of cellular secretion, is crucial for hormone release.
• Intracellular calcium ions (Ca2+) act as key signaling molecules in exocytosis.

Purpose of the Study:

• To investigate the simultaneous dynamics of exocytosis and intracellular Ca2+ in single rat gonadotrophs.
• To determine the modulatory effects of oestradiol-17 beta (E2) on GnRH- and depolarization-stimulated exocytosis.
• To elucidate the mechanism by which E2 influences the Ca2+-dependent exocytotic process.

Main Methods:

• Simultaneous measurement of exocytosis (membrane capacitance) and intracellular Ca2+ (fura-2 fluorescence) in single anterior pituitary gonadotrophs.
• Perforated-patch whole-cell recording technique.
• Culture of cells with or without E2, followed by stimulation with GnRH or membrane depolarization.

Main Results:

• Exocytosis response to GnRH showed a spectrum dependent on intracellular Ca2+ patterns, modeled by a kinetic approach.
• E2 treatment significantly increased GnRH-evoked exocytosis (3-fold) and depolarization-evoked exocytosis (38%) without affecting intracellular Ca2+ responses.
• E2's modulatory effects on exocytosis may involve altered Ca2+ sensitivity or preferential clustering of secretory granules.

Conclusions:

• E2 enhances gonadotroph exocytosis, particularly GnRH-stimulated secretion, independent of changes in intracellular Ca2+ levels.
• The mechanism of E2 action likely involves modulating the Ca2+ sensitivity of the exocytotic machinery or granule localization.
• Maximum E2 effects on exocytosis necessitate the activation of GnRH-dependent signaling pathways, suggesting a complex regulatory interplay.