Medium hyperosmolarity depresses thyrotropin-releasing hormone-induced Ca2+ influx and prolactin secretion in GH4C1 cells.
We studied the influence of graded degrees of hyperosmolarity on the dynamics of the thyrotropin-releasing hormone (TRH)-induced rise in cytosol Ca2+ concentration ([Ca2+]i) and prolactin (PRL) secretion in GH4C1 cells. TRH caused two phases of increase in [Ca2+]i that were differentially altered by hyperosmolarity: 100% hyperosmolarity (600 mOsm) depressed only 20% of an initial high-amplitude [Ca2+]i burst (first phase) dependent on Ca2+ mobilized from intracellular pools, but it abolished a sustained low-amplitude second phase dependent on extracellular Ca2+ influx. Low degrees of hyperosmolarity suppressed PRL secretion due to Ca2+ influx while high degrees suppressed secretion due to mobilized Ca2+. These data suggest that in GH4C1 cells hypertonic inhibition of secretion may result from both blocking Ca2+ influx and mechanisms unrelated to [Ca2+]i.
Sato
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Department of Medicine, Oregon Health Sciences University, Portland 97201.
Wang
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X
Greer
M A
MA
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D009994:Osmolar Concentration; D010911:Pituitary Neoplasms; D011388:Prolactin / Q000378:metabolism*; D013973:Thyrotropin-Releasing Hormone / Q000502:physiology*; D014407:Tumor Cells, Cultured
D013973:Thyrotropin-Releasing Hormone; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D011388:Prolactin; D002118:Calcium