title: Modulators of the protein kinase C system influence biliary excretion of cationic drugs.
abstract: To investigate whether hepatobiliary transport of organic cations is under regulatory control, we studied transport of tri-n-butylmethylammonium in the isolated perfused rat liver and in isolated rat hepatocytes. Transport was investigated in the presence of modulators of the protein kinase C and the cyclic AMP second-messenger system. In the isolated perfused rat liver, it was observed that compounds modulating protein kinase C activity clearly affected the biliary excretion process of the cation tri-n-butylmethylammonium. Phorbol 12-myristate 13-acetate, a compound that directly stimulates protein kinase C, elevated the biliary excretion rate of tri-n-butylmethylammonium in a concentration-dependent manner, reaching a twofold increase at 60 nmol/L of the phorbol ester. The inactive derivative 4 alpha-phorbol 12, 13-didecanoate (60 nmol/L) did not show any effect. Vasopressin (48 nmol/L), a receptor-mediated activator of protein kinase C, stimulated the excretion rate of the cation by about 50%. Staurosporin (1 mumol/L), an inhibitor of protein kinase C, clearly decreased the biliary excretion rate of the cation and also blocked its stimulation by phorbol 12-myristate 13-acetate. Neither phorbol 12-myristate 13-acetate nor vasopressin (at concentrations ranging from 10(-9) to 10(-6) mol/L) affected the initial uptake velocity of tri-n-butylmethylammonium in isolated hepatocytes and isolated perfused livers, whereas staurosporin (1 mumol/L) showed only a modest inhibition of the uptake of the cation. It is inferred that the effect of protein kinase C modulators on hepatobiliary transport of organic cations occurs at the level of carrier-mediated transport in the canalicular membrane.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Pharmacology and Therapeutics, Groningen State University, The Netherlands.
authors.forename: H
authors.initials: H
authors.lastname: Steen
authors.forename: H
authors.initials: H
authors.lastname: Smit
authors.forename: A
authors.initials: A
authors.lastname: Nijholt
authors.forename: M
authors.initials: M
authors.lastname: Merema
authors.forename: D K
authors.initials: DK
authors.lastname: Meijer
mesh_terms: D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D001646:Bile / Q000378:metabolism*; D001693:Biological Transport, Active / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism; D002412:Cations; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D005934:Glucagon / Q000494:pharmacology; D066298:In Vitro Techniques; D008099:Liver / Q000166:cytology / Q000378:metabolism; D008297:Male; D010477:Perfusion; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000644:Quaternary Ammonium Compounds / Q000493:pharmacokinetics*; D051381:Rats; D017208:Rats, Wistar; D015290:Second Messenger Systems; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014667:Vasopressins / Q000494:pharmacology
chemical_list: D000470:Alkaloids; D002352:Carrier Proteins; D002412:Cations; D000644:Quaternary Ammonium Compounds; D014667:Vasopressins; D005576:Colforsin; C043902:tri-n-butylmethylammonium; D005934:Glucagon; D000242:Cyclic AMP; D011493:Protein Kinase C; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate