Endocrinology, Vol 135, 1084-1092, Copyright © 1994 by Endocrine Society

ARTICLES

Characteristics of the Ca2+ spike and oscillations induced by different doses of thyrotropin-releasing hormone (TRH) in individual pituitary cells and nonexcitable cells transfected with TRH receptor complementary deoxyribonucleic acid

EJ Nelson and PM Hinkle
Department of Pharmacology, University of Rochester School of Medicine and Dentistry, New York 14642.

The Ca2+ response of individual cells to TRH was investigated in excitable pituitary GH3 and in nonexcitable Hela cells transfected with the TRH receptor complementary DNA (HelaR cells). GH3 cells typically responded to 1 microM TRH with an immediate transient [Ca2+]i spike (mean peak [Ca2+]i = 1.5 microM) followed by a period of inactivity of approximately 100 sec long and then a secondary increase in [Ca2+]i with oscillations. At 10-100 nM TRH, the initial [Ca2+]i spike was more prolonged and immediately followed by a sustained elevation of [Ca2+]i. At 0.5-1 nM TRH, there was a variable lag before any response; the initial [Ca2+]i spike was absent or small, but the sustained phase was still present. The second phase of elevated [Ca2+]i, which could be eliminated with nimodipine or chelation of extracellular Ca2+, gave a bell-shaped TRH dose response curve. The effect of TRH on Ca2+ oscillations depended both on TRH concentration and the basal oscillation frequency. HelaR cells responded to 1 microM TRH with a rapid [Ca2+]i spike, and at less than or equal to 10 nM TRH, up to 50% of HelaR cells displayed agonist-induced sinusoidal [Ca2+]i oscillations independent of extracellular Ca2+. TRH never caused a sustained elevation of [Ca2+]i in HelaR cells. For GH3 and HelaR cells, the peak [Ca2+]i response increased with TRH concentration up to 1 microM. In contrast, the duration of the initial [Ca2+]i spike was shorter at higher TRH concentrations, decreasing from 16 to 6.3 s (GH3) or 92 to 35 s (HelaR) between 0.5 nM and 1 microM TRH. This shortening of the spike duration was caused by rapid clearing of cytoplasmic Ca2+ that depended primarily on agonist concentration. In summary, TRH stimulates a complex [Ca2+]i response pattern dependent upon both the agonist concentration and cell context. The initial burst of Ca2+ is cleared in part by agonist dependent Ca2+ clearing.

This article has been cited by other articles:

				L. B. Cook and P. M. Hinkle Fate of Internalized Thyrotropin-Releasing Hormone Receptors Monitored with a Timer Fusion Protein Endocrinology, July 1, 2004; 145(7): 3095 - 3100. [Abstract] [Full Text] [PDF]

				C.-C. Zhu, L. B. Cook, and P. M. Hinkle Dimerization and Phosphorylation of Thyrotropin-releasing Hormone Receptors Are Modulated by Agonist Stimulation J. Biol. Chem., July 26, 2002; 277(31): 28228 - 28237. [Abstract] [Full Text] [PDF]

				V. A. Romoser, T. K. Graves, D. Wu, H. Jiang, and P. M. Hinkle Calcium Responses to Thyrotropin-Releasing Hormone, Gonadotropin-Releasing Hormone and Somatostatin in Phospholipase C{beta}3 Knockout Mice Mol. Endocrinol., January 1, 2001; 15(1): 125 - 135. [Abstract] [Full Text]

				R. Yu and P. M. Hinkle Signal Transduction and Hormone-dependent Internalization of the Thyrotropin-releasing Hormone Receptor in Cells Lacking Gq and G11 J. Biol. Chem., May 28, 1999; 274(22): 15745 - 15750. [Abstract] [Full Text] [PDF]

				A. C. Charles, E. T. Piros, C. J. Evans, and T. G. Hales L-type Ca2+ Channels and K+ Channels Specifically Modulate the Frequency and Amplitude of Spontaneous Ca2+ Oscillations and Have Distinct Roles in Prolactin Release in GH3 Cells J. Biol. Chem., March 12, 1999; 274(11): 7508 - 7515. [Abstract] [Full Text] [PDF]

				R. Yu and P. M. Hinkle Signal Transduction, Desensitization, and Recovery of Responses to Thyrotropin-Releasing Hormone after Inhibition of Receptor Internalization Mol. Endocrinol., May 1, 1998; 12(5): 737 - 749. [Abstract] [Full Text]

				C. Villalobos, W. J. Faught, and L. S. Frawley Dynamic Changes in Spontaneous Intracellular Free Calcium Oscillations and Their Relationship to Prolactin Gene Expression in Single, Primary Mammotropes Mol. Endocrinol., January 1, 1998; 12(1): 87 - 95. [Abstract] [Full Text]

				R. Yu and P. M. Hinkle Desensitization of Thyrotropin-releasing Hormone Receptor-mediated Responses Involves Multiple Steps J. Biol. Chem., November 7, 1997; 272(45): 28301 - 28307. [Abstract] [Full Text] [PDF]

				A. Lachowicz, F. Van Goor, A. C. Katzur, G. Bonhomme, and S. S. Stojilkovic Uncoupling of Calcium Mobilization and Entry Pathways in Endothelin-stimulated Pituitary Lactotrophs J. Biol. Chem., November 7, 1997; 272(45): 28308 - 28314. [Abstract] [Full Text] [PDF]

				V. A. Romoser, P. M. Hinkle, and A. Persechini Detection in Living Cells of Ca2+-dependent Changes in the Fluorescence Emission of an Indicator Composed of Two Green Fluorescent Protein Variants Linked by a Calmodulin-binding Sequence. A NEW CLASS OF FLUORESCENT INDICATORS J. Biol. Chem., May 16, 1997; 272(20): 13270 - 13274. [Abstract] [Full Text] [PDF]