Protein kinase C agonists inhibit bile secretion independently of effects on the microcirculation in the isolated perfused rat liver

Abstract

The role of hormones in the regulation of bile secretion is not known; however vasoactive agents, which act via the phosphoinositide signal transduction pathway, may mediate changes in bile flow by altering the hepatic microvasculature. We therefore examined the effects of phorbol esters and diacylglycerol, agonists of the protein kinase C branch of the phosphoinositide cascade, on perfusion pressure and bile flow in a single-pass, hemoglobin-free, isolated perfused rat liver system with constant perfusate flow. The active phorbol ester, 12,13-phorbol dibutyrate, produced a dose-dependent (maximal effect at 10(-6) M), sustained and reversible decrease in bile flow from 1.09 +/- 0.18 to 0.61 +/- 0.09 microliters per min per gm liver (37.2 +/- 5.9%) while simultaneously increasing perfusion pressure from 12.3 +/- 0.7 to 21.5 +/- 2.5 cm H2O (74.0 +/- 4.3%). Both effects were inhibited by the synthetic protein kinase C antagonist H-7. 1,2-Dioctanoyl-sn-glycerol, a diacylglycerol, produced changes in bile flow and perfusion pressure that were similar to, but more marked than, those caused by 12,13-phorbol dibutyrate, whereas the inactive phorbol ester 4 alpha-phorbol didecanoate and the vehicle dimethyl sulfoxide had no effects on either parameter. 12,13-Phorbol dibutyrate infusion resulted in reversible decreases in oxygen consumption (23.3%) and a reversible vascular redistribution of trypan blue dye but did not alter hepatic venous effluent concentrations of K+.(ABSTRACT TRUNCATED AT 250 WORDS)

Tauroursodeoxycholic acid stimulates hepatocellular exocytosis and mobilizes extracellular Ca++ mechanisms defective in cholestasis.

“…Livers were preloaded with HRP (0.05 mg/ml) for 25 perfused with KRB solution (gassed with 95% 02/5% C02) containing 1.9 mM Ca"+ at a constant flow (3.6-4.0 ml/min x g liver). In a first "loading period" livers were perfused in a recirculating way with KRB containing 0.05 mg/ml HRP.…”

Ca2+-dependent Protein Kinase C Isoforms Induce Cholestasis in Rat Liver

“…PMA activates Ca 2ϩ -dependent and Ca 2ϩ -independent, but not atypical PKCs (41). In this study, two inhibitors of PKC with different affinities for cPKCs and nPKCs were used to investigate the PMA-induced cholestasis (11,13). The inhibitor Gö6976 with high selectivity for cPKCs compared with nPKCs (28)) had a stronger inhibitory effect on PMA-induced cholestasis than Gö6850.…”

“…Several studies related cholestasis to the action of protein kinase C (PKC) 1 (11)(12)(13). The first PKC isoform was isolated by Nishizuka (14).…”

Vasopressin-induced disruption of actin cytoskeletal organization and canalicular function in isolated rat hepatocyte couplets: Possible involvement of protein kinase C

“…41,[44][45][46] Furthermore, in addition to the effect on actin conformation, PKC activation was reported to induce changes in other major cytoskeletal elements such as intermediate filament proteins [47][48][49] and tubulin. 42 Finally, PKC was reported to have a role in hepatocyte apoptosis induced by a number of compounds such as the bile salt, glycochenodeoxycholate, 50 [2][3][4] Dissipation of osmotic gradients induced by an increase of ''leakiness'' of the paracellular barrier appears to play a key role in this phenomenon. Indeed, VP as well as a number of agents affecting Ca 2ϩ mobilization such as the Ca 2ϩ -ionophore, A23187, and the inhibitor of microsomal Ca 2ϩ sequestration, t-butyl-benzohydroquinone, were all shown to increase tightjunctional permeability in both isolated perfused rat liver 4,[7][8][9] and in isolated rat hepatocyte couplets.…”