Phosphatidic acid modulates Cl- secretion in T84 cells: varying effects depending on mode of stimulation.
Cl- secretion in T84 cells evoked by a stimulus that activates protein kinase C, carbachol, was associated with elevated levels of 32P-labeled phosphatidic acid (PA). PA's role in the regulation of Cl- secretion was explored by examining the effect of exogenous PA (10(-4) M) on Cl- secretion and intracellular Ca2+ levels ([Ca2+]i) in monolayers. PA potentiated the effect of carbachol on [Ca2+]i and Cl- secretion, although it did not stimulate Cl- secretion by itself. PA had divergent effects on cyclic nucleotide-dependent Cl- secretion. It delayed Cl- secretion induced by vasoactive intestinal polypeptide [VIP, adenosine 3',5'-cyclic monophosphate (cAMP) dependent] but potentiated that induced by the heat-stable enterotoxin of Escherichia coli (STa; guanosine 3',5'-cyclic monophosphate dependent). PA did not alter AMP or GMP levels, suggesting that PA acts at a site distal to the generation of these second messengers. PA caused a slight increase in phosphorylation of protein kinase C substrates but not of cAMP-dependent protein kinase substrates. However, PA is probably not acting through a classical protein kinase C pathway, because we have previously shown that phorbol esters inhibit carbachol's actions, and the protein kinase C inhibitor staurosporine failed to block the effect of PA on VIP- or STa-stimulated Cl- secretion. Thus PA differentially regulates stimulated Cl- secretion in T84 cells, depending on the nature of the agonist.
Vajanaphanich
M
M
Department of Medicine, School of Medicine, University of California, San Diego 92103.
Kachintorn
U
U
Barrett
K E
KE
Cohn
J A
JA
Dharmsathaphorn
K
K
Traynor-Kaplan
A
A
D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D002712:Chlorides / Q000378:metabolism*; D002855:Chromatography, Thin Layer; D003110:Colonic Neoplasms; D000242:Cyclic AMP / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D015180:Electrophoresis, Gel, Two-Dimensional; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007295:Inositol Phosphates / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D010712:Phosphatidic Acids / Q000378:metabolism* / Q000494:pharmacology*; D019269:Phosphatidylinositol 4,5-Diphosphate; D010716:Phosphatidylinositols / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism*; D010750:Phosphoproteins / Q000302:isolation & purification / Q000378:metabolism; D010766:Phosphorylation; D014407:Tumor Cells, Cultured; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology
D002712:Chlorides; D007295:Inositol Phosphates; D010712:Phosphatidic Acids; D019269:Phosphatidylinositol 4,5-Diphosphate; D010716:Phosphatidylinositols; D010743:Phospholipids; D010750:Phosphoproteins; D014660:Vasoactive Intestinal Peptide; D002217:Carbachol; D000242:Cyclic AMP; D002118:Calcium