title: Characterization of phorbol ester- and diacylglycerol-stimulated secretion in permeable GH3 pituitary cells. Interaction with Ca2+.
abstract: Prolactin (PRL) release in permeable GH3 pituitary cells was stimulated by the protein kinase C activators 12-O-tetradecanoylphorbol 13-acetate (TPA) and 1-oleoyl-2-acetyl-sn-glycerol (OAG). Both agents stimulated secretion at 10 nM Ca2+, but higher [Ca2+] (greater than 0.1 microM) potentiated TPA and OAG action. Maximal potentiation occurred at 1 microM calculated free Ca2+, and a similar value was obtained when the cytoplasmic [Ca2+] was measured with the Ca2+-sensitive dye Quin 2. Release of a secretory sulfated proteoglycan was also stimulated by TPA and OAG in permeable GH3 cells, with characteristics similar to those for PRL release. Trifluoroperazine, polymyxin B, neomycin, and 8-(diethylamino)octyl-3,4,5-trimethoxybenzoate all inhibited both TPA- and Ca2+-stimulated PRL release, but in each case the half-maximal inhibitory concentrations were approximately 2-fold higher for TPA-stimulated release compared to Ca2+-stimulated release. Thyrotropin-releasing hormone (TRH) and guanosine 5'-Q-thiotriphosphate, which stimulate polyphosphoinositide breakdown in permeable cells, were found to be only weak stimulators of PRL release, compared to TPA and exogenous diacylglycerol. However, a much stronger effect of TRH was seen if cells were briefly treated with TRH prior to permeabilization. PRL release from TRH-pretreated permeable cells resembled TPA- and OAG-stimulated secretion, with [Ca2+] greater than 0.1 microM potentiating the effect of TRH pretreatment. These studies support the hypothesis that PRL release in GH3 cells can be stimulated directly by a diacylglycerol-activated secretory mechanism whose activity is modulated by [Ca2+].
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002460:Cell Line; D002463:Cell Membrane Permeability; D004075:Diglycerides / Q000494:pharmacology*; D004357:Drug Synergism; D005989:Glycerides / Q000494:pharmacology*; D007700:Kinetics; D010704:Phorbols / Q000494:pharmacology*; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols / Q000378:metabolism; D010911:Pituitary Neoplasms / Q000378:metabolism*; D011388:Prolactin / Q000378:metabolism*; D011509:Proteoglycans / Q000378:metabolism*; D051381:Rats; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
chemical_list: D004075:Diglycerides; D005989:Glycerides; D010704:Phorbols; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; D011509:Proteoglycans; C038237:1-oleoyl-2-acetylglycerol; D011388:Prolactin; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium