Evidence for TRH-induced influx of extracellular Ca2+ in pituitary GH4C1 cells.
The aim of the study was to investigate the relationship between thyrotropin-releasing hormone (TRH)-induced changes in intracellular free Ca2+ ([Ca2+]i), and influx of extracellular Ca2+ in Fura 2 loaded pituitary GH4C1 cells. Stimulating the cells with TRH in a Ca(2+)-containing buffer induced a biphasic change in [Ca2+]i. First, a transient increase in [Ca2+]i, followed by a sustained phase. In cells stimulated with TRH in a Ca(2+)-free buffer, the transient increase in [Ca(2+)]i was decreased (p less than 0.05), and the sustained phase was totally abolished. Addition of Ni2+ prior to TRH blunted the component of the TRH-induced transient increase in [Ca2+]i dependent on influx of Ca2+. In the presence of extracellular Mn2+, TRH stimulated quenching of Fura 2 fluorescence. This quenching was blocked by Ni2+. The results indicate that both the TRH-induced transient increase in [Ca2+]i as well as the sustained phase in [Ca2+]i in GH4C1 cells is dependent on influx of extracellular Ca2+.
Törnquist
K
K
Endocrine Research Laboratory, University of Helsinki, Finland.
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D004072:Digitonin / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004492:Edetic Acid / Q000494:pharmacology; D016257:Fura-2; D007700:Kinetics; D008345:Manganese / Q000494:pharmacology; D009532:Nickel / Q000494:pharmacology; D009553:Nimodipine / Q000494:pharmacology; D010902:Pituitary Gland; D051381:Rats; D013050:Spectrometry, Fluorescence; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*
D008345:Manganese; D009553:Nimodipine; D013973:Thyrotropin-Releasing Hormone; D009532:Nickel; D004492:Edetic Acid; D004072:Digitonin; D002118:Calcium; D016257:Fura-2