Functional uncoupling between intracellular calcium dynamics and secretion in the αT3-1 gonadotropic cell line

✍ Scribed by Citlali Trueta; Mauricio Díaz; Luis A. Vaca; Carmen Clapp; Gonzalo Martíinez De La Escalera

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 293 KB
• Volume: 179
• Category: Article
• ISSN: 0021-9541
• DOI: 10.1002/(sici)1097-4652(199906)179:3<347::aid-jcp12>3.0.co;2-j

✦ Synopsis

Gonadotropin releasing hormone (GnRH) stimulates both transcription and secretion of the ␣ subunit of the gonadotropins in a Ca 2ϩ -dependent fashion. In this study, we examined the role of Ca 2ϩ as the signal coupling agonist occupancy of GnRH receptors to hormone secretion using the gonadotropic cell line ␣T3-1. Treatment of ␣T3-1 cells for 60 min with GnRH (0.1-100 nM), veratridine (50 M) or high K ϩ (56 mM) was completely ineffective in stimulating secretion. The lack of effect occurred in spite of a robust, specific, and dose-dependent biphasic [Ca 2ϩ ] i response consisting of a rapid peak sensitive to thapsigargin (200 nM) followed by a smaller plateau sensitive to the extracellular application of EGTA (5 mM). On the other hand, treatment of ␣T3-1 cells with the Ca 2ϩ ionophore ionomycin resulted in a significant dose-dependent stimulation of secretion and [Ca 2ϩ ] i responses comparable to those elicited by GnRH. Binding assays revealed the presence of Ins(1,4,5)P 3 receptors (Kd ϭ 3.2 nM, Bmax ϭ 50.5 fmol/mg protein) but not ryanodine receptors in ␣T3-1 cell membranes. Together, these results show a functional uncoupling between the [Ca 2ϩ ] i response and secretion in this cell line, suggesting that the increase in [Ca 2ϩ ] i triggered by GnRH and depolarization may be necessary but not sufficient to stimulate exocytosis.