Regulation of mucin secretion in T84 adenocarcinoma cells by forskolin: relationship to Ca2+ and PKC.
The relationship between the adenosine 3',5'-cyclic monophosphate-mediated protein kinase A (PKA)-dependent stimulatory pathway for mucin secretion and Ca(2+)-mediated and protein kinase C (PKC)-mediated secretion was studied in T84 cells, using the postreceptor secretagogues forskolin, A-23187, and phorbol 12-myristate 13-acetate (PMA), the protein kinase inhibitors staurosporine and 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7), high- and low-Ca2+ media, and the Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA). Staurosporine (10(-5) M) inhibited both PMA and forskolin at their maximally effective concentrations, whereas H-7 (5 x 10(-5) M) inhibited only PMA. Stimulation of mucin secretion by forskolin (5 x 10(-5) M) was not significantly affected by the reduction of medium Ca2+ to 47 and 129 nM, equivalent to published values for intracellular Ca2+ concentration ([Ca2+]i). Stimulation by forskolin was reduced by preloading cells with BAPTA, but to a much smaller extent than Ca(2+)-dependent stimulation by A-23187. A-23187-mediated mucin secretion from BAPTA-loaded cells was augmented by high doses of forskolin. Similar concentrations of forskolin had no effect on A-23187-stimulated secretion in calcium-replete cells. Our results indicate that forskolin does not stimulate mucin secretion by increasing Ca2+ entry or releasing Ca2+ from intracellular stores. Forskolin can stimulate mucin secretion in a Ca(2+)-independent manner but is apparently inhibited by high levels of intracellular Ca2+ induced by Ca2+ ionophores in 1.0 mM Ca2+ media.(ABSTRACT TRUNCATED AT 250 WORDS)
Forstner
G
G
Research Institute, Hospital for Sick Children, Toronto, Canada.
Zhang
Y
Y
McCool
D
D
Forstner
J
J
D000230:Adenocarcinoma / Q000378:metabolism* / Q000473:pathology; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D005576:Colforsin / Q000494:pharmacology*; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D005110:Extracellular Space / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D009077:Mucins / Q000378:metabolism*; D011493:Protein Kinase C / Q000502:physiology*; D014407:Tumor Cells, Cultured
D009077:Mucins; D005576:Colforsin; D004533:Egtazic Acid; D011493:Protein Kinase C; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium