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Functional uncoupling between intracellular calcium dynamics and secretion in the αT3‐1 gonadotropic cell line
Author(s) -
Trueta Citlali,
Díaz Mauricio,
Vaca Luis A.,
Clapp Carmen,
Martíinez De La Escalera Gonzalo
Publication year - 1999
Publication title -
journal of cellular physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.529
H-Index - 174
eISSN - 1097-4652
pISSN - 0021-9541
DOI - 10.1002/(sici)1097-4652(199906)179:3<347::aid-jcp12>3.0.co;2-j
Subject(s) - ionomycin , medicine , thapsigargin , endocrinology , secretion , veratridine , ryanodine receptor , biology , receptor , intracellular , extracellular , stimulation , calcium in biology , gonadotropin releasing hormone , chemistry , microbiology and biotechnology , hormone , luteinizing hormone , sodium , sodium channel , organic chemistry
Gonadotropin releasing hormone (GnRH) stimulates both transcription and secretion of the α subunit of the gonadotropins in a Ca 2+ ‐dependent fashion. In this study, we examined the role of Ca 2+ as the signal coupling agonist occupancy of GnRH receptors to hormone secretion using the gonadotropic cell line αT3‐1. Treatment of αT3‐1 cells for 60 min with GnRH (0.1–100 nM), veratridine (50 μM) or high K + (56 mM) was completely ineffective in stimulating secretion. The lack of effect occurred in spite of a robust, specific, and dose‐dependent biphasic [Ca 2+ ] 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 αT3‐1 cells with the Ca 2+ ionophore ionomycin resulted in a significant dose‐dependent stimulation of secretion and [Ca 2+ ] i responses comparable to those elicited by GnRH. Binding assays revealed the presence of Ins(1,4,5)P 3 receptors (Kd = 3.2 nM, Bmax = 50.5 fmol/mg protein) but not ryanodine receptors in αT3‐1 cell membranes. Together, these results show a functional uncoupling between the [Ca 2+ ] i response and secretion in this cell line, suggesting that the increase in [Ca 2+ ] i triggered by GnRH and depolarization may be necessary but not sufficient to stimulate exocytosis. J. Cell. Physiol. 179:347–357, 1999. © 1999 Wiley‐Liss, Inc.