Transient but not oscillating component of the calcium mobilizing response to gonadotropinreleasing hormone depends on calcium influx in pituitary gonadotrophs

Estradiol Modulation of GNRH-Stimulated LH Release in Rat Anterior Pituitary Cells: Involvement of Dihydropyridine-Sensitive Calcium Channels

“…Some authors, however, do not agree [ 18]. Recently our group has confirmed the implica tion of PKC in the action of GnRH, but this effect was related to treatment of the cells by E2 [19,20], It has also been demonstrated that binding of GnRH to its receptor results in an increase in intracellular calcium ([Ca2 + ]i), which initiates events such as hormone secretion [21,22], This has been confirmed more recently by several studies using fluorescence analysis on gonadotroph populations [23][24][25] or in single gonadotroph cells [26][27][28][29]. Also, GnRH-induced [Ca2 + ]i increase was greater when cells were treated by E2 and this increase was affected by extra cellular calcium [30], [Ca2 + ]i increase in gonadotroph cells occurs through two major mechanisms: (i) mobilization of Ca2+ from in tracellular bound stores [10,31] and (ii) the influx of cal cium [32] across the plasma membrane via the voltagesensitive calcium channels (VSCC).…”

Cell Networks in Endocrine/Neuroendocrine Gland Function

“…The relationship between intracellular calcium and secretion has long been recognised (350), and the calcium response of endocrine cells to stimulation can be used as a surrogate for hormone output in a number of endocrine organs where Ca 2+ fluxes are closely associated with quantal secretory granule release such as pituitary cells (372,393). Examples of studies utilizing calcium imaging to monitor endocrine cell activity are those showing the existence of multiple functional states of lactotrophs with the calcium indicator dye indo-1 (243), the complex concentration-dependent calcium response in gonadotropin-releasing hormone-stimulated individual gonadotrophs (158), the oscillatory activity in response to stimulation and inhibition of isolated somatotrophs with fura-2 (416) and the generation of coordinated population responses in pancreatic beta cells (352). While first phase insulin secretion is Ca 2+ -dependent, changes in second phase insulin secretion are not necessarily accompanied by changes in intracellular Ca 2+ concentration (172), although studies with better spatiotemporal resolution are required to confirm this.…”

Novel Aspects of GnRH‐Induced Intracellular Signaling and Secretion in Pituitary Gonadotrophs

“…In contrast, a variable rate of spiking (5-30 spikes min-') is consistent and characteristic feature of agoniststimulated gonadotrophs ( 5 2 , 68). Although several studies in gonadotrophs have demonstrated that calcium spiking frequency is controlled by GnRH and InsP, concentration (49), others have suggested that the amplitude rather than the frequency of Ca2+ spiking is controlled by agonist concentration (69). The latter report implies that single cells cannot modulate their frequency of spiking in response to two different agonist concentrations, but respond with either baseline oscillatory or biphasic Ca2+ signaling, and that the percentage of cells showing one or other type of response varies during the estrous cycle.…”