Mechanism of spontaneous intracellular calcium fluctuations in single GH4C1 rat pituitary cells

• Published in: Biochemical journal 1993-05, Vol.292 (1), p.175-182
• Main Authors: WAGNER, K. A, YACONO, P. W, GOLAN, D. E, TASHJIAN, A. H
• Format: Article
• Language: English
• Subjects: 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester - pharmacology; Animals; Biological and medical sciences; Calcium - metabolism; Cell physiology; Cells, Cultured; Fundamental and applied biological sciences. Psychology; Membrane and intracellular transports; Membrane Potentials; Molecular and cellular biology; Pituitary Gland - cytology; Pituitary Gland - drug effects; Pituitary Gland - metabolism; Rats; Thyrotropin-Releasing Hormone - pharmacology
• ISSN: 0264-6021; 1470-8728
• DOI: 10.1042/bj2920175

Individual unstimulated GH4C1 cells exhibited spontaneous dynamic fluctuations in cytosolic free Ca2+ concentration ([Ca2+]i). Either chelation of extracellular Ca2+ with EGTA or treatment with nifedipine inhibited spontaneous [Ca2+]i fluctuations, indicating that the [Ca2+]i profile was dependent on the entry of extracellular Ca2+ via voltage-operated Ca2+ channels (VOCC). Spontaneous [Ca2+]i fluctuations did not resume immediately after exposure of EGTA-pretreated cells to extracellular Ca2+, supporting the hypothesis that the complex [Ca2+]i profiles observed in unstimulated cells required filling of an intracellular Ca2+ pool. BAY K 8644 elicited large rapid oscillations in [Ca2+]i. After chelation of extracellular Ca2+, however, re-addition of Ca2+ plus BAY K 8644 did not result in [Ca2+]i oscillations. The intracellular Ca2+ pool necessary for BAY K-induced oscillations was not the same Ins(1,4,5)P3-sensitive pool stimulated by thyrotropin-releasing hormone (TRH), because the TRH-stimulated Ins(1,4,5)P3-induced [Ca2+]i spike and the BAY K 8644-induced oscillations were differentially sensitive to chelation of extracellular Ca2+ and thapsigargin. Caffeine caused an increase in [Ca2+]i fluctuations in quiescent cells, supporting a role for Ca(2+)-induced Ca2+ release (CICR) in the generation of spontaneous [Ca2+]i fluctuations. In conclusion, the complex spontaneous changes in [Ca2+]i observed in single GH4C1 cells depend on both the influx of extracellular Ca2+ through VOCC and the action of an intracellular Ca2+ pool that increases [Ca2+]i through a CICR-like mechanism.