Multiple alterations of canalicular. membrane transport activities in rats with CCL4-induced hepatic injury

The influence of CCl4-induced experimental hepatic injury (CCl4-EHI) on the expression and transport activities of primary active transporters on,the canalicular membrane, including P-glycoprotein (P-gp), a bile salt export pump (Bsep) and a multidrug resistance associated protein2 (Mrp2), was assessed. CCl4-EHI was induced by an intraperitoneal injection of CCl4 to rats at a dose of 1 ml/kg 24 h prior to the preparation of canalicular liver plasma membrane (cLPM) vesicles and pharmacokinetic studies. The expression of each transporter was measured for the vesicles via Western blot analysis at 6, 12, 24, 36, and 48 h after the injection of CCl4. The in vivo canalicular excretion clearance (CLexc) Of [H-3]daunomycin, [H-3]taurocholate and [H-3]17beta-estradiol-17beta-D-glucuronide (E(2)17betaG), representative substrates of P-gp, Bsep, and Mrp2, respectively, was determined following an i.v. infusion to rats. The uptake of each substrate into cLPM vesicles in the presence of ATP was also measured by a rapid filtration technique. As the result of the CCl4-EHI, the protein level of transporters was altered as a function of time in multiple manners; it was increased by 3.6-fold for P-gp, unchanged for Bsep, and decreased by 73% for Mrp2 at 24 h. The in vivo CLexc and the intrinsic uptake clearance into cLPM vesicles (CLint) at 24 h after the CCl4 injection (CCl4-EHI24 (h)) were also influenced by the EHI in a similar manner; they were increased by 1.8- and 1.9-fold for daunomycin, unchanged for taurocholate, and decreased by 41 and 39% for E(2)17betaG, respectively, consistent with multiple alterations in the expression of the relevant transporters.