Cell swelling inhibits proteolysis in perfused rat liver

Abstract

Exposure of isolated single-pass-perfused rat liver to hypo-osmotic media resulted in liver cell swelling and an inhibition of release of branched-chain amino acids. Similarly, cell swelling inhibited [3H]leucine release from perfused livers from rats in which liver proteins were prelabelled in vivo by intraperitoneal injection of L-[4,5-3H]leucine 16-20 h before the experiment. The effects of cell swelling on [3H]leucine release were fully reversible. [3H]Leucine release was also inhibited when cell swelling was induced by addition of glutamine (0.5-2 mM). There was a close relationship between the inhibition of [3H]leucine release and the degree of liver cell swelling, regardless of whether cell swelling was induced by hypo-osmotic perfusion or addition of glutamine. The data suggest that the known anti-proteolytic effect of glutamine is in large part due to glutamine-induced hepatocyte swelling.

Cell Swelling and the sensitivity of autophagic proteolysis to inhibition by amino acids in isolated rat hepatocytes

“…Although amino acids are known to be inhibitors of hepatic autophagic proteolysis, very little information is available regarding the mechanism by which they exert this effect [32, 331. In their stimulating studies on the control of proteolysis in the isolated perfused liver, Haussinger and coworkers [7,[9][10][11] recently proposed that the increase in cell volume following amino-acid influx is in part responsible for the inhibition of proteolysis by amino acids. They not only demonstrated that perfusion with hypo-osmotic media was able to mimic the anti-proteolytic effect of amino acids, but also that the inhibitory effect of several amino acids (but not all of them) could be directly attributed to their ability to induce cell swelling.…”

“…In the experiments of Haussinger et al [ 9 ] , cycloheximide was not used and rates of proteolysis were measured either as the production of leucine from non-labelled livers or as ['Hlleucine from previously labelled liver protein in the presence of non-labelled (0.1 mM) leucine in order to prevent reincorporation of the label into protein. In our experiments, we used cycloheximide to inhibit simultaneous protein synthesis.…”

Involvement of Integrins and Src in Insulin Signaling toward Autophagic Proteolysis in Rat Liver

“…The portal pressure was routinely monitored with a pressure transducer (Hugo Sachs Electronics, Hugstetten, Germany) (20). The effluent K ϩ concentration was continuously monitored with a K ϩ -sensitive electrode (Radiometer, Munich, Germany); insulin-induced K ϩ fluxes were determined by planimetry of areas under curves (21). If not stated otherwise, the compounds used in this study did not affect portal perfusion pressure.…”

“…Likewise, the Src inhibitor PP-2 but not its inactive analogue PP-3 prevented proteolysis inhibition by insulin (Fig. 3B, Table II 3 H label release into effluent was monitored as a measure of hepatic proteolysis in liver perfusion experiments (21). Because of differences in the labeling of the animals in vivo, the release of radioactivity was set to 100% during control conditions in the identical perfusion experiment.…”

“…Rat Liver-The rate of proteolysis was assessed by measuring the release of 3 H from isolated perfused rat livers after prelabeling of liver proteins in vivo by intraperitoneal injection of 150 Ci of L- [4, H]leucine 16 -20 h before the perfusion experiment (21). After a pre-perfusion period of 80 min, the release of trichloroacetic acid soluble 3 H label reached a steady state (about 500 cpm min Ϫ1 g liver Ϫ1 ) and was associated with effluent leucine by more than 95% as shown by chromatographic analysis (15).…”