Control of hepatic proteolysis by amino acids

Hallbrucker, Christian; Dahl, Stephan Vom; Läng, Florian; Häussinger, Dieter

doi:10.1111/j.1432-1033.1991.tb15963.x

Cited by 81 publications

(69 citation statements)

References 40 publications

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“…As autophagic proteolysis is strongly dependent on lysosomal pH, the intravesicular alkalinization observed here could well participate in the anti-proteolytic effects of cell swelling after treatment with glutamine, barium and reduction of extracellular osmolarity (Haussinger et al, 1990a(Haussinger et al, , 1991Hallbrucker et al, alkalinization occurring after cell swelling is not restricted to a minor portion of acidic compartments. As lysosomes constitute a major portion of acidic intracellular compartments (Tager et al, 1988), it appears very unlikely that intravesicular alkalinization following cell swelling does not include lysosomes.…”

Section: Discussionmentioning

confidence: 96%

“…The intracellular mechanisms mediating this effect, however, have remained elusive until recently, when it has been recognized that cell swelling, as it occurs during the concentrative uptake of amino acids, markedly inhibits proteolysis (Hiiussinger et al, 1990b(Hiiussinger et al, , 1991 Hiiussinger and Lang, ,b, 1992Hallbrucker et al, 1991a). It has been shown that the anti-proteolytic effect of glutamine, for instance, is fully mimicked by proportionate cell swelling due to reduction of the extracellular osmolarity or inhibition of the action of K+ channels in the cell membrane (Hiiussinger et al, 1990b(Hiiussinger et al, , 1991Lang, 1991a,b, 1992).…”

Section: Introductionmentioning

confidence: 99%

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Effect of cell volume on Acridine Orange fluorescence in hepatocytes

Völkl

Friedrich

Häussinger

et al. 1993

Biochemical Journal

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Hepatic proteolysis is inhibited by cell swelling following a variety of experimental manoeuvres, such as reduction of extracellular osmolarity, concentrative uptake of amino acids, or blockade of K+ channels by barium. On the other hand, proteolysis is known to be accomplished by pH-sensitive lysosomal proteases. Accordingly, NH3/NH4+ inhibits proteolysis by intralysosomal alkalinization. The present study has been performed to test for an effect of cell volume on the pH of acidic intracellular compartments, as assessed by Acridine Orange fluorescence at > 520 nm (F > 520). F > 520 is enhanced by NH3/NH4+ (2 and 20 mmol/l respectively), by glutamine (2 mmol/l), by the K(+)-channel blocker barium (10 mmol/l) and by reduction of extracellular osmolarity (by 20 and 80 mosmol/l respectively). The observations point to release of Acridine Orange from acidic cellular compartments, which is indicative of alkalinization of these compartments during cell swelling. This effect may contribute to the regulation of proteolysis.

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Section: Discussionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

Effect of cell volume on Acridine Orange fluorescence in hepatocytes

Völkl

Friedrich

Häussinger

et al. 1993

Biochemical Journal

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“…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.…”

Section: Discussionmentioning

confidence: 99%

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

Meijer

Gustafson

Luiken

et al. 1993

European Journal of Biochemistry

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In the isolated perfused rat liver, autophagic proteolysis is inhibited by hypo-osmotic perfusion media [Haussinger, D., Hallbrucker, C . , vom Dahl, S., Lang, F. & Gerok, W. (1990) Biochem. J. 272, 239-2421. Here we report that in isolated hepatocytes, incubated in the absence of amino acids to ensure maximal proteolytic flux, proteolysis was not inhibited by hypo-osmolarity while the synthesis of glycogen from glucose, a process known to be very sensitive to changes in cell volume [Baquet, A., Hue, L., Meijer, A. J., van Woerkom, G. M. & Plomp, P. J. A. M. (1990) J. B i d . Chein. 265, 955 -9591, was stimulated under identical conditions. However, in isolated hepatocytes, hypo-osmolarity increased the sensitivity of autophagic proteolysis to inhibition by low concentrations of amino acids. The anti-proteolytic effect of hypo-osmolarity in our experiments was not due to stimulation of amino-acid transport into the hepatocytes: neither the consumption of most amino acids, nor the rate of urea synthesis was appreciably affected by hypo-osmotic incubation conditions. In the course of these studies we also found that hypo-osmolarity increased the affinity of protein synthesis for amino acids.In the presence of amino acids the intracellular level of ATP was not much affected. However, because of cell swelling under these conditions the intracellular concentration of ATP decreased. It is proposed that a small part of the inhibition of proteolysis by amino acids may be due to this fall in ATP concentration.Evidence is rapidly accumulating that an increase in the volume of hepatocytes, in response either to intracellular amino acid accumulation or to a decrease in the osmolarity of the extracellular fluid, has anabolic and anti-catabolic effects. Thus, an increase in cell volume results in increased glycogen synthesis [l, 21, increased lipogenesis [3, 41, increased polyamine synthesis [5], increased metabolism of some amino acids [6, 71, and in decreased glycogenolysis [8].Haussinger and coworkers [9-111 demonstrated that in the isolated perfused rat liver an increase in cell volume also inhibited protein breakdown and that this phenomenon could account for, at least in part, the well known property of some amino acids to inhibit this process. However, Car0 [12] showed that in isolated rat hepatocytes, an increase in cell volume did not inhibit proteolysis, or even slightly stimulated it, when flux through the autophagic pathway was maximal, i.e. in the absence of added amino acids. Intrigued by this puzzling difference in results, which was not discussed [ll], we decided to investigate this property of isolated hepatocytes in more detail. We have now found in rat hepatocytes that, although a decrease in medium osmolarity per se does not appreciably affect proteolysis, it does increase the sensitivity of proteolysis to inhibition by amino acids. MATERIALS AND METHODSRat hepatocytes were isolated from 20-24-h fasted male Wistar rats (200-250 g) as in [13].Hepatocytes (5 mg dry cells/ml) were incubated in closed 25-ml p...

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“…Hepatic proteolysis is under the control of amino acids, hormones ( [1][2][3][4]; for reviews see [5,6]) and liver cell volume [7,8]. The mechanisms underlying proteolysis control by amino acids and hormones are not understood [6]; however, recent evidence points to an involvement of cell volume alterations [7][8][9].…”

Section: Introductionmentioning

confidence: 99%

“…The mechanisms underlying proteolysis control by amino acids and hormones are not understood [6]; however, recent evidence points to an involvement of cell volume alterations [7][8][9]. The anti-proteolytic effects of glutamine and glycine could be fully mimicked by equipotent hypo-osmotic cell swelling [7,8], and the inhibition of proteolysis by other amino acids could, at least in part, be ascribed to amino acid-induced cell swelling [8]. The anti-proteolytic effect of insulin in liver parallels the extent of hormone-induced intracellular K+ accumulation, even when the insulin-induced K+ uptake was modulated by the nutritional state or a variety of inhibitors [9].…”

Section: Introductionmentioning

confidence: 99%

Regulation of liver cell volume and proteolysis by glucagon and insulin

Dahl

Hallbrucker

Läng

et al. 1991

Biochemical Journal

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The effects of insulin and glucagon on liver cell volume and proteolysis were studied in isolated perfused rat liver. The rate of proteolysis was assessed as [3H]leucine release from single-pass-perfused livers from rats which had been prelabelled in vivo by intraperitoneal injection of [3H]leucine. The intracellular water space was determined from the wash-out profiles of simultaneously added [3H]inulin and [14C]urea. In normo-osmotic (305 mosM) control perfusions the intracellular water space was 548 +/- 10 microliters/g wet mass (n = 44) and was increased by 16.5 +/- 2.6% (n = 6), i.e. by 85 +/- 14 microliters/g, after hypoosmotic exposure (225 mosM). Glucagon (0.1 microM) decreased the intracellular water space by 17 +/- 4% (n = 4), whereas insulin (35 nM) increased the intracellular water space by 9.3 +/- 1.4% (n = 15). Also, in isolated rat hepatocyte suspensions insulin (100 nM) caused cell swelling by 10.7 +/- 1.8% (n = 16), which was fully reversed by glucagon. In perfused liver, insulin-induced cell swelling was accompanied by a hepatic net K+ uptake (4.5 +/- 0.2 mumol/g) and an inhibition of proteolysis by 21 +/- 2% (n = 12); further addition of glucagon led to a net K+ release of 3.8 +/- 0.2 mumol/g (n = 7) and fully reversed the insulin effects on both cell volume and proteolysis. Similarly, insulin-induced cell swelling and inhibition of proteolysis were completely antagonized by hyperosmotic (385 mosM) cell shrinkage. Furthermore, cell swelling and inhibition of proteolysis after hypo-osmotic exposure or amino acid addition were reversed by glucagon-induced cell shrinkage. There was a close relationship between the extent of cell swelling and the inhibition of proteolysis, regardless of whether cell volume was modified by insulin, glucagon or aniso-osmotic exposure. The data show that glucagon and insulin are potent modulators of liver cell volume, at least in part by alterations of cellular K+ balance, and that their opposing effects on hepatic proteolysis can largely be explained by opposing effects on cell volume. It is hypothesized that hormone-induced alterations of cell volume may represent an important, not yet recognized, mechanism mediating hormonal effects on metabolism.

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Control of hepatic proteolysis by amino acids

Cited by 81 publications

References 40 publications

Effect of cell volume on Acridine Orange fluorescence in hepatocytes

Effect of cell volume on Acridine Orange fluorescence in hepatocytes

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

Regulation of liver cell volume and proteolysis by glucagon and insulin

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