Effects of monensin on vesicular transport pathways in the perfused rat liver

Abstract

In the rat hepatocyte, the internalization and degradation of asialoglycoproteins and the secretion of plasma and biliary proteins require specific intracellular sorting of vesicles. To aid in the biochemical characterization of these different vesicular pathways, we examined the effects of the ionophore monensin on the uptake and degradation of 125I-asialoorosomucoid (ASOR) and on the secretion of plasma and biliary proteins by the in situ perfused rat liver. In control livers, 77% of injected 125I-ASOR was extracted on first pass; 93% of the extracted radioactivity was released back into the circulation (totally degraded and some intact ASOR was found); and approximately 2% was recovered in the bile, some of which was intact. Monensin treatment decreased first pass uptake of 125I-ASOR to 57% and abruptly blocked the release of radioactivity into the perfusate and the bile. When hepatic proteins were biosynthetically labeled with 3H-leucine, monensin treatment dramatically reduced and delayed the secretion of newly synthesized proteins into both the perfusate and the bile. In contrast with control livers, in which secretion of protein into the perfusate preceded secretion of protein into the bile, TCA-precipitable 3H-protein appeared in bile about 20 min before TCA-precipitable 3H-protein appeared in the perfusate in monensin-treated livers. Thus, monensin treatment in the perfused liver blocked the degradation of asialoglycoproteins and inhibited the secretion of plasma proteins but had less effect on biliary protein secretion. These data document physiologic effects of monensin in an intact organ and suggest that biochemical distinctions between different vesicular pathways exist in the rat hepatocyte.

Effects of monensin on ATP levels and cell functions in rat liver and lung in vitro

“…In its more advanced phase, as seen after 60 min at 38~ with 1 /J,M monensin, the vesiculation appeared very similar to that noted in liver slices from young, post-natal rats [18], in peffused liver [13] and in isolated hepatocytes [30] at similar concentrations, as well as in several other tissue preparations (references in Introduction). Similar vesiculation of Golgi elements was also noted in at least two types of cells in the fetal lung, epithelial type II cells and macrophages.…”

“…At 1 ].LM monensin, a concentration often used by other workers, [4,13,18,22,31,34,35], very few vesicles were seen after 15 rain at 38~ (Fig. 2) and Golgi elements could be recognized only occasionally (Fig.…”

Mathematical Analysis of Hepatic High Density Lipoprotein Transport Based on Quantitative Imaging Data

“…About 2-5% of radioactively labeled ASOR perfused into rat liver is secreted into the bile within a 30-min chase (25)(26)(27). In primate liver about 7% of perfused ASOR become released into the bile after a 47-min chase (28).…”

Monensin and14C oleic acid absorption in the rat

“…Moreover several works reported a strong decrease of secretory pathways provoked by monensin (Tartakoff 1983, Melin etal. 1984, Kloppel et al 1986). In conclusion monensin, by its selective action on enterocyte organelles involved in fatty acid absorption, strongly impaired chylomicron formation and oleic acid absorption in the rat.…”

“…Golgi apparatus appears to be an essential step for the final construction, particularly glycosylation of lipoproteins before their transfer through secretory vesicles towards lateral plasma membranes and their exocytosis in all the intercellular spaces. Monensin was shown to have a specific action on the one hand on the Golgi apparatus of absorptive cells in vivo (Ellinger and Pavelka 1984) and in vitro (Danielsen et al 1983) and on the other hand on intracellular transport, particularly vesicular traffic and secretion (Tartakoff 1983, Kloppel et al 1986), all organdies and cellular functions involved in lipid absorption.…”