Effect of lysosomotropic agents on the taurocholate-stimulated biliary excretion of horseradish peroxidase

Abstract

The effects of the lysosomotropic agents chloroquine and leupeptin on the taurocholatestimulated biliary excretion of horseradish peroxidase (HRP) was studied in bile fistula rats. HRP (0.5 mg/100 g body wt) was injected into the portal vein during taurocholate (0.4 μmol/min/100 g body wt) or saline infusion. HRP appeared in bile showing both an early (approx. 5 min) and a late (approx. 25 min) excretion peak. The late peak, which represented about 95% of the total HRP excreted, is due to transcellular vesicular transport. The early peak is mainly due to paracellular leakage although a rapid vesicular transport also contributes. Taurocholate infusion significantly increased the biliary output of HRP (both peaks) and of the endogenous lysosomal enzyme acid phosphatase. Pretreatment with chloroquine or leupeptin inhibited the taurocholate-stimulated late excretion of HRP into bile, without affecting its early excretion. The lysosomotropic agents did not affect the biliary excretion of bile salts but significantly inhibited the taurocholate-stimulated biliary excretion of acid phosphatase. The results are consistent with a role of lysosomes in the taurocholate-stimulated major transcellular vesicular transport of HRP into bile.