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D Häussinger

Publications and source records attributed to D Häussinger.

At least 19 recordsLinked to original sources
PubMed1992

Cell volume and bile acid excretion.

The interaction between cell volume and taurocholate excretion into bile was studied in isolated perfused rat liver. Cell swelling due to hypo-osmotic exposure, addition of amino acids or insulin stimulated taurocholate excretion into bile and bile flow, whereas hyperosmotic cell shrinkage inhibited these. These effects were explained by changes in Vmax of taurocholate excretion into bile: Vmax. increased from about 300 to 700 nmol/min per g after cell swelling by 12-15% caused by either hypo-osmotic exposure or addition of amino acids under normo-osmotic conditions. Steady-state taurocholate excretion into bile was not affected when the influent K+ concentration was increased from 6 to 46 mM or decreased to 1 mM with iso-osmoticity being maintained by corresponding changes in the influent Na+ concentration. Replacement of 40 mM-NaCl by 80 mM-sucrose decreased taurocholate excretion into bile by about 70%; subsequent hypo-osmotic exposure by omission of sucrose increased taurocholate excretion to 160%. Only minor, statistically insignificant, effects of aniso-osmotic cell volume changes on the appearance of bolus-injected horseradish peroxidase in bile were observed. Taurocholate (400 microM) exhibited a cholestatic effect during hyperosmotic cell shrinkage, but not during hypo-osmotic cell swelling. Both taurocholate and tauroursodeoxycholate increased liver cell volume. Tauroursodeoxycholate stimulated taurocholate (100 microM) excretion into bile. This stimulatory effect was strongly dependent on the extent of tauroursodeoxycholate-induced cell swelling. During continuous infusion of taurocholate (100 microM) further addition of tauroursodeoxycholate at concentrations of 20, 50 and 100 microM increased cell volume by 10, 8 and 2% respectively, in parallel with a stimulation of taurocholate excretion into bile by 29, 27 and 9% respectively. There was a close relationship between the extent of cell volume changes and taurocholate excretion into bile, regardless of whether cell volume was modified by tauroursodeoxycholate, amino acids or aniso-osmotic exposure. The data suggest that: (i) liver cell volume is one important factor determining bile flow and biliary taurocholate excretion; (ii) swelling-induced stimulation of taurocholate excretion into bile is probably not explained by alterations of the membrane potential; (iii) bile acids modulate liver cell volume; (iv) taurocholate-induced cholestasis may depend on cell volume; (v) stimulation of taurocholate excretion into bile by tauroursodeoxycholate can largely be explained by tauroursodeoxycholate-induced cell swelling.

Amino Acids↗
PubMed1992

Hepatocyte swelling leads to rapid decrease of the G-/total actin ratio and increases actin mRNA levels.

Exposure of isolated rat hepatocytes to hypotonic (190 mosmol/l) incubation media lowered the cellular G-actin level without affecting the total actin content: here the G-/total actin ratio decreased by 15.5 +/- 1.4% (n = 7). Similar effects were observed following isotonic cell swelling by either addition of glutamine (10 mM) or insulin (100 nM), resulting in a decrease of the G-/total actin ratios by 13.5 +/- 2.1% (n = 5) and 14.1 +/- 1.1% (n = 11), respectively. The effects of hypotonic exposure, glutamine and insulin on the G-/total actin ratio largely occurred within 1 min and persisted for at least 2 h in presence of the respective effectors. After a 120 min exposure to hypotonic media, glutamine or insulin the actin mRNA levels were increased 2.4-, 2.0- and 3.6-fold, respectively. Hypertonic exposure lowered the G-/total actin ratio by only 4.9 +/- 2.5% (n = 4) and increased actin mRNA levels only 1.2-fold. There was a close relationship between glutamine- and hypotonicity-induced cell swelling and the decrease of G-/total actin ratios. The data suggest that cell swelling exerts rapid and marked effects on the state of actin polymerization and increases actin mRNA levels. Thus, cytoskeletal alterations in response to cell swelling may be involved in the regulation of hepatic metabolism by cell volume.

Actins↗
PubMed1992

Liver cell volume and protein synthesis.

Protein synthesis in isolated rat hepatocytes was determined from the incorporation of [3H]leucine (4 mM) into acid-precipitable material in the presence of amino acids at twice their physiological concentration. Protein synthesis increased linearly with time and incubated cell protein, and was inhibited by cycloheximide by more than 95%. In normo-osmotic incubations containing amino acids at twice the physiological concentration the rate of [3H]leucine incorporation was 5.8 +/- 0.2 nmol/h per mg of cell protein (n = 26). Hyperosmotic cell shrinkage due to addition of 60 mM-NaCl or 120 mM-raffinose inhibited [3H]leucine incorporation into acid-precipitable material by 60 and 74% respectively, whereas hypo-osmotic cell swelling was ineffective. Inhibition of protein synthesis by adding 120 mM-raffinose was largely counteracted by simultaneous lowering of the NaCl concentration by 60 mM. Glutamine (10 mM) had no effect on protein synthesis in normo-osmotic incubations (320 mosM), but stimulated protein synthesis in hyperosmotically (440 mosM) pre-shrunken cells almost to rates found in normo-osmotic (320 mosM) control incubations. Cyclic AMP and vasopressin inhibited protein synthesis by 23% and 8% respectively, whereas insulin and phenylephrine were ineffective. However, inhibition of protein synthesis by cyclic AMP was about twice as strong in the presence of vasopressin or phenylephrine. When protein synthesis was preinhibited by cyclic AMP, [3H]leucine incorporation was stimulated by glutamine (10 mM), insulin or hypo-osmotic exposure. There was a close relationship between the inhibition of protein synthesis and the extent of hepatocyte shrinkage induced by the above-mentioned effectors, suggesting a role of cell volume in the regulation of hepatic protein synthesis.

Animals↗
PubMed1992

Effect of anisotonic cell-volume modulation on glutathione-S-conjugate release, t-butylhydroperoxide metabolism and the pentose-phosphate shunt in perfused rat liver.

1. Addition of 1-chloro-2,4-dinitrobenzene to isolated perfused rat liver results in the rapid formation of its glutathione-S-conjugate [S-(2,4-dinitrophenyl)glutathione], which is released into both, bile and effluent perfusate. Anisotonic perfusion did not affect total S-conjugate formation, but release of the S-conjugate into the perfusate was increased (decreased) following hypertonic (hypotonic) exposure at the expense of excretion into bile. Stimulation of S-conjugate release into the perfusate following hypertonic exposure paralleled the time course of volume-regulatory net K+ uptake. 2. Basal steady-state release of oxidized glutathione (GSSG) into bile was 1.30 +/- 0.12 nmol.g-1.min-1 (n = 18) during normotonic (305 mOsmol/l) perfusion and was 3.8 +/- 0.3 nmol.g-1.min-1 in the presence of t-butylhydroperoxide (50 mumol/l). Hypotonic exposure (225 mOsmol/1) lowered both, basal and t-butylhydroperoxide (50 mumol/l)-stimulated GSSG release into bile by 35% and 20%, respectively, whereas hypertonic exposure (385 mOsmol/l) increased. Anisotonic exposure was without effect on t-butylhydroperoxide removal by the liver. GSSG release into bile also decreased by 33% upon liver-cell swelling due to addition of glutamine plus glycine (2 mmol/l, each). 3. Hypotonic exposure led to a persistent stimulation 14CO2 production from [1-14C]glucose by about 80%, whereas 14CO2 production from [6-14C]glucose increased by only 10%. Conversely, hypertonic exposure inhibited 14CO2 production from [1-14C]glucose by about 40%, whereas 14CO2 production from [6-14C]glucose was unaffected. The effect of anisotonicity on 14CO2 production from [1-14C]glucose was also observed in presence of t-butylhydroperoxide (50 mumol/l), which increased 14CO2 production from [1-14C]glucose by about 40%. 4. t-Butylhydroperoxide (50 mumol/l) was without significant effect on volume-regulatory K+ fluxes following exposure to hypotonic (225 mOsmol/l) or hypertonic (385 mOsmol/l) perfusate. Lactate dehydrogenase release from perfused rat liver under the influence of t-butylhydroperoxide was increased by hypertonic exposure compared to hypotonic perfusions. 5. The data suggest that hypotonic cell swelling stimulates flux through the pentose-phosphate pathway and diminishes loss of GSSG under conditions of mild oxidative stress. Hypotonically swollen cells are less prone to hydroperoxide-induced lactate dehydrogenase release than hypertonically shrunken cells. Hypertonic cell shrinkage stimulates the excretion of glutathione-S-conjugates into the sinusoidal circulation at the expense of biliary secretion.

Animals↗
PubMed1992

Effects of bradykinin on cell volume and intracellular pH in NIH 3T3 fibroblasts expressing the ras oncogene.

BCECF fluorescence has been applied to determine intracellular pH (pHi) in NIH 3T3 fibroblasts expressing the Ha-ras oncogene (+ras) and otherwise identical cells not expressing the oncogene (-ras). In +ras cells, pHi is significantly more alkaline (6.79 +/- 0.03 n = 12) than in -ras cells (6.64 +/- 0.02, n = 8). Bradykinin (100 nmol/l) leads to intracellular alkalinization in both +ras (to 6.96 +/- 0.04, n = 12) and -ras cells (to 6.85 +/- 0.02, n = 8). The effect of bradykinin is completely abolished in the presence of dimethylamiloride (100 mumol/l), which does not modify pHi in the absence of bradykinin. Similar to bradykinin, cell shrinkage by addition of 15 mmol/l NaCl to the extracellular fluid leads to intracellular alkalinization (by 0.08 +/- 0.01, n = 15). Cell volume is significantly greater in +ras cells (2.7 +/- 0.4 pl, n = 15) than in -ras cells (2.2 +/- 0.4 pl, n = 15). Bradykinin leads to cell shrinkage in both +ras cells (by 7 +/- 1%, n = 17) and -ras cells (by 5 +/- 1%, n = 15). The effect of bradykinin on cell volume can be reversed by the reduction of extracellular NaCl concentration by 15 mmol/l NaCl in +ras cells and by 7 mmol/l NaCl in -ras cells. This maneuver completely abolishes (in -ras cells) or blunts (in +ras cells) the alkalinizing effect of bradykinin. In conclusion, +ras cells are more alkaline than -ras cells. Bradykinin leads to further intracellular alkalinization by activation of the Na+/H(+)-exchanger, at least in part secondary to hormone-induced cell shrinkage.

3T3 Cells↗
PubMed1992

Biosynthesis and excretion of gangliosides by the isolated perfused rat liver.

De novo synthesis and excretion into perfusate and bile fluid of hepatic gangliosides were studied in isolated perfused rat livers. Addition of N-acetyl-[6-3H(n)]D-mannosamine to the perfusate resulted in radioactive synthesis of at least eight gangliosides labeled in their sialic acid residues. About 10% of total de novo synthesized gangliosides were excreted into the perfusate, less than 1% into the bile fluid. Labeled gangliosides were tentatively identified by cochromatography with known standards. All of them are known to occur in rat liver and sera. The results indicate that most, if not all, normal serum gangliosides are synthesized in the liver; excretion with bile fluid is negligible. They explain previous observations, and indicate clinical implications, which are discussed.

Animals↗
PubMed1992

Cell swelling increases bile flow and taurocholate excretion into bile in isolated perfused rat liver.

The effects of aniso-osmotically and amino-acid-induced cell-volume changes on bile flow and biliary taurocholate excretion were studied in isolated perfused rat liver. With taurocholate (100 microM) in the influent perfusate, hypo-osmotic exposure (225 mosmol/l) increased taurocholate excretion into bile and bile flow by 42 and 27% respectively, whereas inhibition by 32 and 47% respectively was observed after hyperosmotic (385 mosmol/l) exposure. The effects of aniso-moticity on taurocholate excretion into bile was observed throughout aniso-osmotic exposure, even after completion of volume-regulatory ion fluxes and were fully reversible upon re-exposure to normo-osmotic media. Hypo-osmotic cell swelling (225 mosmol/l) increased the Vmax. of taurocholate translocation from the sinusoidal compartment into bile about 2-fold. Also, cell swelling induced by glutamine and glycine stimulated both bile flow and biliary taurocholate excretion. There was a close relationship between the aniso-osmotically and amino-acid-induced change of cell volume and taurocholate excretion into bile. The data suggest that liver cell volume plays an important role in regulating bile-acid-dependent bile flow and biliary taurocholate excretion.

Amino Acids↗
PubMed1992

Metabolic alkalosis as driving force for urea synthesis in liver disease: pathogenetic model and therapeutic implications.

Despite a marked reduction of the urea cycle capacity, patients with well-compensated chronic liver disease excrete near-normal amounts of urea. Compensation of the urea cycle defect apparently occurs through the activation of liver glutaminase, as suggested by an inverse relationship between the in vitro ureagenic capacity and the flux through glutaminase in liver tissue from patients with a normal, fatty, or cirrhotic liver. In these patients, the flux through glutaminase, as determined in vitro, increases in parallel with the plasma bicarbonate level and plasma pH determined in vivo. In view of this and results from previous studies, the following hypothesis is suggested: The decrease of urea cycle enzyme activities in liver cirrhosis produces metabolic alkalosis due to an impaired bicarbonate elimination. Alkalosis in turn activates and stabilizes hepatic glutaminase and accordingly mitochondrial ammonia provision for carbamoylphosphate synthetase. This results in a compensatory stimulation of the urea cycle flux in the cirrhotic patient to near-normal rates, despite the marked reduction of urea cycle enzyme activity. Accordingly, alkalosis is an important driving force for urea synthesis in the cirrhotic patient. With respect to clinical medicine, attention must be paid to acid-base disturbances in the hyperammonemic patient.

Alkalosis↗
PubMed1992

Altered cell volume regulation in ras oncogene expressing NIH fibroblasts.

Expression of the Ha-ras oncogene has been reported to stimulate the dimethylamiloride sensitive Na+/H+ exchanger and Na+,K+,2Cl- cotransport, both transport systems which are involved in cell volume regulation. The present study has been performed to test for an influence of ras oncogene expression on cell volume regulation in NIH 3T3 fibroblasts expressing the Ha-ras oncogene (+ ras). As controls served NIH 3T3 fibroblasts not expressing the ras oncogene (-ras). In isotonic extracellular fluid, the cell volume of + ras cells (2.70 +/- 0.08 pl) is significantly greater than the cell volume of -ras cells (2.04 +/- 0.10 pl). Both, + ras and -ras cells exhibit a regulatory cell volume increase in hypertonic extracellular fluid and a regulatory cell volume decrease in hypotonic extracellular fluid. The regulatory cell volume decrease is inhibited by 1 mmol/l quinidine and barium, the regulatory cell volume increase is inhibited in -ras and +ras cells by dimethyl-amiloride (100 mumol/l) and, only in +ras cells, by furosemide (100 mumol/l) and bumetanide (10 mumol/l). In conclusion, expression of the ras oncogene leads to a shift of the set point for cell volume regulation to greater cell volumes, which may contribute to the activation of the Na+/H+ exchanger and Na+,K+,2Cl- cotransport.

3T3 Cells↗
PubMed1992

Hepatic regulation of renal function.

Despite apparently conflicting reports in the past, the bulk of evidence presently available points to a significant role for the liver in the regulation of renal function. Hepatic regulation of renal function may involve both a hepatorenal reflex and a liver-borne diuretic factor (LBDF and/or 'glomerulopressin'). The hepatorenal reflex is elicited by an increase in intrahepatic pressure, and/or certain amino acids in portal venous blood. It is transmitted by serotonin in the liver and presumably by noradrenaline in the kidney. It leads to a marked decrease in renal blood flow, glomerular filtration and urinary flow rate. The evidence for the LBDF is still circumstantial. The LBDF may be stimulated by glucagon and adenosine. It leads to a marked increase of renal blood flow, glomerular filtration rate and urinary output. Amongst the conditions presumed to be associated with altered hepatic regulation of renal function are postprandial hyperfiltration, and the deterioration of renal function which occurs in liver disease, cardiac insufficiency and cardiovascular shock.

Amino Acids↗
PubMed1992

Hepatocyte heterogeneity in the metabolism of amino acids and ammonia.

With respect to hepatocyte heterogeneity in ammonia and amino acid metabolism, two different patterns of sublobular gene expression are distinguished: 'gradient-type' and 'strict- or compartment-type' zonation. An example for strict-type zonation is the reciprocal distribution of carbamoylphosphate synthase and glutamine synthase in the liver lobule. The mechanisms underlying the different sublobular gene expressions are not yet settled but may involve the development of hepatic architecture, innervation, blood-borne hormonal and metabolic factors. The periportal zone is characterized by a high capacity for uptake and catabolism of amino acids (except glutamate and aspartate) as well as for urea synthesis and gluconeogenesis. On the other hand, glutamine synthesis, ornithine transamination and the uptake of vascular glutamate, aspartate, malate and alpha-ketoglutarate are restricted to a small perivenous hepatocyte population. Accordingly, in the intact liver lobule the major pathways for ammonia detoxication, urea and glutamine synthesis, are anatomically switched behind each other and represent in functional terms the sequence of the periportal low affinity system (urea synthesis) and a previous high affinity system (glutamine synthesis) for ammonia detoxication. Perivenous glutamine synthase-containing hepatocytes ('scavenger cells') act as a high affinity scavenger for the ammonia, which escapes the more upstream urea-synthesizing compartment. Periportal glutaminase acts as a pH- and hormone-modulated ammonia-amplifying system in the mitochondria of periportal hepatocytes. The activity of this amplifying system is one crucial determinant for flux through the urea cycle in view of the high Km (ammonia) of carbamoylphosphate synthase, the rate-controlling enzyme of the urea cycle. The structural and functional organization of glutamine and ammonia-metabolizing pathways in the liver lobule provides one basis for the understanding of a hepatic role in systemic acid base homeostasis. Urea synthesis is a major pathway for irreversible removal of metabolically generated bicarbonate. The lobular organization enables the adjustment of the urea cycle flux and accordingly the rate of irreversible hepatic bicarbonate elimination to the needs of the systemic acid base situation, without the threat of hyperammonemia.

Amino Acids↗
PubMed1992

Anisoosmostic liver perfusion: redox shifts and modulation of alpha-ketoisocaproate and glycine metabolism.

1) In isolated perfused rat liver, 14CO2 production from [1-14C]alpha-ketoisocaproate or [1-14C]glycine as well as ketogenesis from alpha-ketoisocaproate were stimulated upon exposure to hypoosmotic perfusion media, whereas hyperosmotic exposure inhibited. The effects of anisotonicity were preserved when ketogenesis from alpha-ketoisocaproate and 14CO2 production from [1-14C]glycine were already stimulated by glucagon. On the other hand, ketogenesis from tyrosine (2 mM) or octanoate (0.1 mM) were almost unaffected by anisoosmotic exposure. 2) With all ketogenic substrates studied, hypoosmotic (hyperosmotic) cell swelling (shrinkage) decreased (increased) the beta-hydroxybutyrate/acetoacetate ratio in effluent perfusate. A shift of the mitochondrial and cytosolic NADH systems to a more oxidized (reduced) state following hypoosmotic (hyperosmotic) exposure was also found upon infusion of beta-hydroxybutyrate/acetoacetate and lactate/pyruvate as redox indicator metabolite couples. The effects of anisotonicity on the beta-hydroxybutyrate/acetoacetate ratio were reversible upon normoosmotic reexposure and persisted throughout anisoosmotic exposure despite completion of volume regulatory K+ fluxes within 10-15 min. Hepatic oxygen consumption decreased by about 10% during hyperosmotic cell shrinkage and was transiently stimulated during hypoosmotic exposure. 3) There was a close relationship between ketogenesis from alpha-ketoisocaproate (0.5 mM) and the mitochondrial redox state, as assessed by the beta-hydroxybutyrate/acetoacetate ratio in effluent, regardless of whether the pathway was modulated by anisotonicity or glucagon. 4) Isoosmotic cell swelling induced by addition of glutamine (3 mM) was without significant effect on ketogenesis from octanoate and stimulated ketogenesis and 14CO2production from [1-14C]alpha-ketoisocaproate only slightly (i.e. by less than 10%); however, in each case the hydroxybutyrate/acetoacetate ratio in effluent perfusate decreased by about 20% upon addition of glutamine. 5) Stimulation of 14CO2production from [1-14C]glycine by hypoosmotic exposure and glucagon was only slightly affected when the accompanying decrease of the beta-hydroxybutyrate/acetoacetate ratio was reversed by addition of beta-hydroxybutyrate. 6) The data are compatible with a hypotonicity (hypertonicity)-induced shift of the mitochondrial NADH system to a more oxidized (reduced) state, probably due to a alterations of respiration. Mitochondrial swelling probably also occurs under the influence of glutamine. Modulation of ketogenesis from alpha-ketoisocaproate, but not of glycine oxidation by anisoosmotic exposure and glucagon can be related to the accompanying redox shifts. The observations support the concept that cell volume may be an important parameter determining liver cell function.

Animals↗
PubMed1992

Liver and systemic pH-regulation.

Traditionally, lungs and kidneys are viewed as principal organs being involved in systemic acid-base homeostasis in mammals, but this view is not entirely compatible with basic principles of chemistry [for reviews see (1-3)]. Accordingly, a new acidbase concept was developed including an important role of the liver. Hepatic urea synthesis is an energy-driven, irreversible neutralization of the strong base HCO3- by the weak acid NH4+ and a potent feed-back regulation circuit adjusts urea cycle flux, i.e. irreversible hepatic HCO3- elimination, to the requirements of the acid base situation. Accordingly, the liver becomes a major organ for maintenance of HCO3- homeostasis and several implications for clinical medicine are derived from this "new" liver function.

Acid-Base Equilibrium↗