Dual effects of a phorbol ester on calcium-dependent chloride secretion by T84 epithelial cells.
Ca(2+)-dependent secretagogues (e.g., carbachol, histamine, ionomycin, and 4-bromo-A23187) have relatively transient effects on chloride secretion, even if there is a sustained increase in cytosolic calcium ([Ca2+]i) (as for the ionophores). Because these agents increase both [Ca2+]i and protein kinase C (PKC) activity, chloride secretion might be stimulated by [Ca2+]i and terminated by PKC activity. We tested the effect of a PKC activator, phorbol 12-myristate 13-acetate (PMA), on Cl- secretion by T84 cell monolayers by measuring short-circuit current (Isc). PMA alone had no effect on Isc but potentiated increases in Isc when added 10 min or less before Ca(2+)-dependent secretagogues. Chelation of [Ca2+]i with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid inhibited the increases both in [Ca2+]i and Isc induced by carbachol with or without brief PMA pretreatment. Longer preincubations with PMA inhibited Isc responses to Ca(2+)-dependent secretagogues, even when increased [Ca2+]i was sustained by ionophores. Inhibitors of PKC could reverse the inhibitory effect of PMA but did not reverse the potentiating effect. The effects of PMA on Cl- secretion were reproduced by 1,2-dioctanoyl-sn-glycerol and were mirrored by effects on K+ channel opening. Thus PMA has dual effects on chloride secretion. Initially, it exerts a stimulatory action and subsequently an inhibitory action. The stimulatory effect only occurs if Ca(2+)-dependent secretion is ongoing. The inhibitory effect of PMA is mediated by PKC and cannot be overcome by increasing [Ca2+]i.
Kachintorn
U
U
Department of Medicine, University of California, San Diego 92103.
Vongkovit
P
P
Vajanaphanich
M
M
Dinh
S
S
Barrett
K E
KE
Dharmsathaphorn
K
K
D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D000470:Alkaloids / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D002460:Cell Line; D002712:Chlorides / Q000378:metabolism*; D003106:Colon / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D007413:Intestinal Mucosa / Q000166:cytology / Q000378:metabolism*; D007546:Isoquinolines / Q000494:pharmacology; D009994:Osmolar Concentration; D010879:Piperazines / Q000494:pharmacology; D047428:Protein Kinase Inhibitors; D012413:Rubidium / Q000378:metabolism; D013110:Sphingosine / Q000494:pharmacology; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D013997:Time Factors
D000470:Alkaloids; D002712:Chlorides; D007546:Isoquinolines; D010879:Piperazines; D047428:Protein Kinase Inhibitors; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D019311:Staurosporine; D012413:Rubidium; D013110:Sphingosine; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium