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A J Meijer

Publications and source records attributed to A J Meijer.

At least 19 recordsLinked to original sources
PubMed2005

Autophagy and signaling: their role in cell survival and cell death.

Macroautophagy is a vacuolar, self-digesting mechanism responsible for the removal of long-lived proteins and damaged organelles by the lysosome. The discovery of the ATG genes has provided key information about the formation of the autophagosome, and about the role of macroautophagy in allowing cells to survive during nutrient depletion and/or in the absence of growth factors. Two connected signaling pathways encompassing class-I phosphatidylinositol 3-kinase and (mammalian) target of rapamycin play a central role in controlling macroautophagy in response to starvation. However, a considerable body of literature reports that macroautophagy is also a cell death mechanism that can occur either in the absence of detectable signs of apoptosis (via autophagic cell death) or concomitantly with apoptosis. Macroautophagy is activated by signaling pathways that also control apoptosis. The aim of this review is to discuss the signaling pathways that control macroautophagy during cell survival and cell death.

Animals↗
PubMed2004

Effect of chronic renal failure with metabolic acidosis on alanine metabolism in isolated liver cells.

BACKGROUND & AIMS: Decreased ureagenesis and gluconeogenesis from alanine have been reported during chronic renal failure in rat. This study addressed the respective roles of plasma-membrane transport and intracellular metabolism in these abnormalities of alanine pathways. METHODS: In hepatocytes isolated from uremic and control rats, we investigated: (1) the influence of uremia on gluconeogenesis and ureagenesis during incubations with alanine; (2) the kinetics of alanine plasma-membrane transport; (3) the relationships between intracellular alanine concentrations and its metabolism. Plasma-membrane alanine transport was assessed after addition of alanine (2 mM) by measuring its intracellular accumulation from 0 to 10 min, in the presence of a transaminase inhibitor. Alanine metabolism was studied in perifused hepatocytes by measuring intracellular alanine concentration together with urea, glucose and lactate production in the presence of increasing concentrations of alanine (0-8 mM). RESULTS: Uremic rats showed decreased plasma bicarbonate. Uremia induced (P<0.05) a decrease in both gluconeogenesis (36%) and ureagenesis (22%). Alanine plasma-membrane transport decreased by 20% during uremia. During perifusions, uremia induced a 30-40% decrease in urea, glucose, and lactate production without modifying intracellular alanine concentration. CONCLUSIONS: In uremic rats with acidosis, hepatocyte alanine utilization was impaired at both plasma-membrane transport and intracellular transamination steps.

Acidosis↗
PubMed2004

Free fatty acids increase hepatic glycogen content in obese males.

Obesity is associated with increased hepatic glycogen content. In vivo and in vitro data suggest that plasma free fatty acids (FFA) may cause this increase. In this study we investigated the effect of physiological plasma FFA levels on hepatic glycogen metabolism by studying intrahepatic glucose pathways in lean and obese subjects. Six lean and 6 obese males were studied twice during a 16- to 22-hour fast, once with and once without acipimox, an inhibitor of lipolysis. Intrahepatic glucose fluxes were measured by infusion of [2-(13C1)]glycerol, [1-(2H1)]galactose, and [U-(13C6)]glucose. Acetaminophen was administered as a glucuronate probe. In both lean and obese control studies, plasma FFA levels increased progressively, whereas acipimox completely suppressed plasma FFA levels for the whole study period. In lean males glycogenolysis did not change in the acipimox study, but decreased in the control study (P < .01). In lean males, neither glycogen synthesis, glycogen synthesis retained as glycogen, nor glycogen balance differed between control and acipimox studies. In obese males glycogenolysis did not change in the acipimox study, but decreased in the control study (P < .01). Glycogen synthesis did not change in either study. Glycogen synthesis retained as glycogen did not change in acipimox study, but increased in the control study (P = .03). Glycogen balance did not change in the acipimox study, but increased in the control study (P < .01). This study demonstrates that in obese males physiological levels of FFA contribute to the retention of hepatic glycogen during short-term fasting by inhibiting breakdown of glycogen and increasing glycogen synthesis retained as glycogen, whereas in lean males this effect was absent due to unaltered glycogen synthesis retained as glycogen.

Adult↗
PubMed2003

Dietary carbohydrate deprivation increases 24-hour nitrogen excretion without affecting postabsorptive hepatic or whole body protein metabolism in healthy men.

Because insulin is an important regulator of protein metabolism, we hypothesized that physiological modulation of insulin secretion, by means of extreme variations in dietary carbohydrate content, affects postabsorptive protein metabolism. Therefore, we studied the effects of three isocaloric diets with identical protein content and low-carbohydrate/high-fat (2% and 83% of total energy, respectively), intermediate-carbohydrate/intermediate-fat (44% and 41% of total energy, respectively), and high-carbohydrate/low-fat (85% and 0% of total energy, respectively) content in six healthy men. Whole body protein metabolism was assessed by 24-h urinary nitrogen excretion, postabsorptive leucine kinetics, and fibrinogen and albumin synthesis by infusion of [1-(13)C]leucine and [1-(13)C]valine. The low-carbohydrate/high-fat diet resulted in lower absorptive and postabsorptive plasma insulin concentrations, and higher rates of nitrogen excretion compared with the other two diets: 15.3 +/- 0.9 vs. 12.1 +/- 1.1 (P = 0.03) and 10.8 +/- 0.5 g/24 h (P = 0.005), respectively. Postabsorptive rates of appearance of leucine and of leucine oxidation were not different among the three diets. In addition, dietary carbohydrate content did not affect the synthesis rates of fibrinogen and albumin. In conclusion, eucaloric carbohydrate deprivation increases 24-h nitrogen loss but does not affect postabsorptive protein metabolism at the hepatic and whole body level. By deduction, dietary carbohydrate is required for an optimal regulation of absorptive, rather than postabsorptive, protein metabolism.

Adult↗
PubMed2001

Fatty acid and amino acid modulation of glucose cycling in isolated rat hepatocytes.

We studied the influence of glucose/glucose 6-phosphate cycling on glycogen deposition from glucose in fasted-rat hepatocytes using S4048 and CP320626, specific inhibitors of glucose-6-phosphate translocase and glycogen phosphorylase respectively. The effect of amino acids and oleate was also examined. The following observations were made: (1) with glucose alone, net glycogen production was low. Inhibition of glucose-6-phosphate translocase increased intracellular glucose 6-phosphate (3-fold), glycogen accumulation (5-fold) without change in active (dephosphorylated) glycogen synthase (GSa) activity, and lactate production (4-fold). With both glucose 6-phosphate translocase and glycogen phosphorylase inhibited, glycogen deposition increased 8-fold and approached reported in vivo rates of glycogen deposition during the fasted-->fed transition. Addition of a physiological mixture of amino acids in the presence of glucose increased glycogen accumulation (4-fold) through activation of GS and inhibition of glucose-6-phosphatase flux. Addition of oleate with glucose present decreased glycolytic flux and increased the flux through glucose 6-phosphatase with no change in glycogen deposition. With glucose 6-phosphate translocase inhibited by S4048, oleate increased intracellular glucose 6-phosphate (3-fold) and net glycogen production (1.5-fold), without a major change in GSa activity. It is concluded that glucose cycling in hepatocytes prevents the net accumulation of glycogen from glucose. Amino acids activate GS and inhibit flux through glucose-6-phosphatase, while oleate inhibits glycolysis and stimulates glucose-6-phosphatase flux. Variation in glucose 6-phosphate does not always result in activity changes of GSa. Activation of glucose 6-phosphatase flux by fatty acids may contribute to the increased hepatic glucose production as seen in Type 2 diabetes.

Adenosine Triphosphate↗
PubMed2001

The tumor suppressor PTEN positively regulates macroautophagy by inhibiting the phosphatidylinositol 3-kinase/protein kinase B pathway.

The tumor suppressor PTEN is a dual protein and phosphoinositide phosphatase that negatively controls the phosphatidylinositol (PI) 3-kinase/protein kinase B (Akt/PKB) signaling pathway. Interleukin-13 via the activation of the class I PI 3-kinase has been shown to inhibit the macroautophagic pathway in the human colon cancer HT-29 cells. Here we demonstrate that the wild-type PTEN is expressed in this cell line. Its overexpression directed by an inducible promoter counteracts the interleukin-13 down-regulation of macroautophagy. This effect was dependent upon the phosphoinositide phosphatase activity of PTEN as determined by using the mutant G129E, which has only protein phosphatase activity. The role of Akt/PKB in the signaling control of interleukin-13-dependent macroautophagy was investigated by expressing a constitutively active form of the kinase ((Myr)PKB). Under these conditions a dramatic inhibition of macroautophagy was observed. By contrast a high rate of autophagy was observed in cells expressing a dominant negative form of PKB. These data demonstrate that the signaling control of macroautophagy overlaps with the well known PI 3-kinase/PKB survival pathway and that the loss of PTEN function in cancer cells inhibits a major catabolic pathway.

Autophagy↗
PubMed2001

Acute inhibition of hepatic glucose-6-phosphatase does not affect gluconeogenesis but directs gluconeogenic flux toward glycogen in fasted rats. A pharmacological study with the chlorogenic acid derivative S4048.

Effects of acute inhibition of glucose-6-phosphatase activity by the chlorogenic acid derivative S4048 on hepatic carbohydrate fluxes were examined in isolated rat hepatocytes and in vivo in rats. Fluxes were calculated using tracer dilution techniques and mass isotopomer distribution analysis in plasma glucose and urinary paracetamol-glucuronide after infusion of [U-(13)C]glucose, [2-(13)C]glycerol, [1-(2)H]galactose, and paracetamol. In hepatocytes, glucose-6-phosphate (Glc-6-P) content, net glycogen synthesis, and lactate production from glucose and dihydroxyacetone increased strongly in the presence of S4048 (10 microm). In livers of S4048-treated rats (0.5 mg kg(-1)min(-)); 8 h) Glc-6-P content increased strongly (+440%), and massive glycogen accumulation (+1260%) was observed in periportal areas. Total glucose production was diminished by 50%. The gluconeogenic flux to Glc-6-P was unaffected (i.e. 33.3 +/- 2.0 versus 33.2 +/- 2.9 micromol kg(-1)min(-1)in control and S4048-treated rats, respectively). Newly synthesized Glc-6-P was redistributed from glucose production (62 +/- 1 versus 38 +/- 1%; p < 0.001) to glycogen synthesis (35 +/- 5% versus 65 +/- 5%; p < 0.005) by S4048. This was associated with a strong inhibition (-82%) of the flux through glucokinase and an increase (+83%) of the flux through glycogen synthase, while the flux through glycogen phosphorylase remained unaffected. In livers from S4048-treated rats, mRNA levels of genes encoding Glc-6-P hydrolase (approximately 9-fold), Glc-6-P translocase (approximately 4-fold), glycogen synthase (approximately 7-fold) and L-type pyruvate kinase (approximately 4-fold) were increased, whereas glucokinase expression was almost abolished. In accordance with unaltered gluconeogenic flux, expression of the gene encoding phosphoenolpyruvate carboxykinase was unaffected in the S4048-treated rats. Thus, acute inhibition of glucose-6-phosphatase activity by S4048 elicited 1) a repartitioning of newly synthesized Glc-6-P from glucose production into glycogen synthesis without affecting the gluconeogenic flux to Glc-6-P and 2) a cellular response aimed at maintaining cellular Glc-6-P homeostasis.

Animals↗
PubMed2001

Dietary fat content alters insulin-mediated glucose metabolism in healthy men.

BACKGROUND: A high dietary fat intake is involved in the pathogenesis of insulin resistance. OBJECTIVE: The aim was to compare the effect of different amounts of dietary fat on hepatic and peripheral insulin sensitivity. DESIGN: Six healthy men were studied on 3 occasions after consuming for 11 d diets with identical energy and protein contents but different percentages of energy as fat and carbohydrate as follows: 0% and 85% [low-fat, high-carbohydrate (LFHC) diet], 41% and 44% [intermediate-fat, intermediate-carbohydrate (IFIC) diet], and 83% and 2% [high-fat, low-carbohydrate (HFLC) diet]. Insulin sensitivity was quantified by using a hyperinsulinemic euglycemic clamp (plasma insulin concentration: approximately 190 pmol/L). RESULTS: During hyperinsulinemia, endogenous glucose production was higher after the HFLC diet (2.5 +/- 0.3 micromol x kg(-1) x min(-1); P < 0.05) than after the IFIC and LFHC diets (1.7 +/- 0.3 and 1.2 +/- 0.4 micromol x kg(-1) x min(-1), respectively). The ratio of dietary fat to carbohydrate had no unequivocal effects on insulin-stimulated glucose uptake. In contrast, insulin-stimulated, nonoxidative glucose disposal tended to increase in relation to an increase in the ratio of fat to carbohydrate, from 14.8 +/- 5.1 to 20.6 +/- 1.9 to 26.2 +/- 2.9 micromol x kg(-1) x min(-1) (P < 0.074 between the 3 diets). Insulin-stimulated glucose oxidation was significantly lower after the HFLC diet than after the IFIC and LFHC diets: 1.7 +/- 0.8 compared with 13.4 +/- 2.1 and 19.0 +/- 2.1 micromol x kg(-1) x min(-1), respectively (P < 0.05). During the clamp study, plasma fatty acid concentrations were higher after the HFLC diet than after the IFIC and LFHC diets: 0.22 +/- 0.02 compared with 0.07 +/- 0.01 and 0.05 +/- 0.01 mmol/L, respectively (P < 0.05). CONCLUSION: A high-fat, low-carbohydrate intake reduces the ability of insulin to suppress endogenous glucose production and alters the relation between oxidative and nonoxidative glucose disposal in a way that favors storage of glucose.

Adult↗
PubMed2001

Acute inhibition of glucose-6-phosphate translocator activity leads to increased de novo lipogenesis and development of hepatic steatosis without affecting VLDL production in rats.

Glucose-6-phosphatase (G6Pase) is a key enzyme in hepatic glucose metabolism. Altered G6Pase activity in glycogen storage disease and diabetic states is associated with disturbances in lipid metabolism. We studied the effects of acute inhibition of G6Pase activity on hepatic lipid metabolism in nonanesthetized rats. Rats were infused with an inhibitor of the glucose-6-phosphate (G6P) translocator (S4048, 30 mg. kg(-1). h(-1)) for 8 h. Simultaneously, [1-(13)C]acetate was administered for determination of de novo lipogenesis and fractional cholesterol synthesis rates by mass isotopomer distribution analysis. In a separate group of rats, Triton WR 1339 was injected for determination of hepatic VLDL-triglyceride production. S4048 infusion significantly decreased plasma glucose (-11%) and insulin (-48%) levels and increased hepatic G6P (201%) and glycogen (182%) contents. Hepatic triglyceride contents increased from 5.8 +/- 1.4 micromol/g liver in controls to 20.6 +/- 5.5 micromol/g liver in S4048-treated animals. De novo lipogenesis was increased >10-fold in S4048-treated rats, without changes in cholesterol synthesis rates. Hepatic mRNA levels of acetyl-CoA carboxylase and fatty acid synthase were markedly induced. Plasma triglyceride levels increased fourfold, but no differences in plasma cholesterol levels were seen. Surprisingly, hepatic VLDL-triglyceride secretion was not increased in S4048-treated rats. These studies demonstrate that inhibition of the G6Pase system leads to acute stimulation of fat synthesis and development of hepatic steatosis, without affecting hepatic cholesterol synthesis and VLDL secretion. The results emphasize the strong interactions that exist between hepatic carbohydrate and fat metabolism.

Animals↗
PubMed2000

Amino-acid-dependent signal transduction.

Recent research carried out in several laboratories has indicated that, in addition to their role as intermediates in many metabolic pathways, amino acids can interact with insulin-dependent signal transduction. In this short review, the current state of this rapidly expanding field is discussed.

Amino Acids↗
PubMed2000

Distinct classes of phosphatidylinositol 3'-kinases are involved in signaling pathways that control macroautophagy in HT-29 cells.

3-Methyladenine which stops macroautophagy at the sequestration step in mammalian cells also inhibits the phosphoinositide 3-kinase (PI3K) activity raising the possibility that PI3K signaling controls the macroautophagic pathway (Blommaart, E. F. C., Krause, U., Schellens, J. P. M., Vreeling-Sindelárová, H., and Meijer, A. J. (1997) Eur. J. Biochem. 243, 240-246). The aim of this study was to identify PI3Ks involved in the control of macroautophagic sequestration in human colon cancer HT-29 cells. An increase of class I PI3K products (phosphatidylinositol 3,4-bisphosphate and phosphatidylinositol 3,4,5-triphosphate) caused by either feeding cells with synthetic lipids (dipalmitoyl phosphatidylinositol 3, 4-bisphosphate and dipalmitoyl phosphatidylinositol 3,4, 5-triphosphate) or by stimulating the enzymatic activity by interleukin-13 reduced macroautophagy. In contrast, an increase in the class III PI3K product (phosphatidylinositol 3-phosphate), either by feeding cells with a synthetic lipid or by overexpressing the p150 adaptor, stimulates macroautophagy. Transfection of a specific class III PI3K antisense oligonucleotide greatly inhibited the rate of macroautophagy. In accordance with a role of class III PI3K, wortmannin (an inhibitor of PI3Ks) inhibits macroautophagic sequestration and protein degradation in the low nanomolar range (IC(50) 5-15 nM). Further in vitro enzymatic assay showed that 3-methyladenine inhibits the class III PI3K activity. Dipalmitoyl phosphatidylinositol 3-phosphate supplementation or p150 overexpression rescued the macroautophagic pathway in HT-29 cells overexpressing a GTPase-deficient mutant of the Galpha(i3) protein suggesting that both class III PI3K and trimeric G(i3) protein signaling are required in the control macroautophagy in HT-29 cells. In conclusion, our results demonstrate that distinct classes of PI3K control the macroautophagic pathway in opposite directions. The roles of PI3Ks in macroautophagy are discussed in the context of membrane recycling.

Adenocarcinoma↗
PubMed2000

The effects of carbohydrate variation in isocaloric diets on glycogenolysis and gluconeogenesis in healthy men.

To evaluate the effect of dietary carbohydrate content on postabsorptive glucose metabolism, we quantified gluconeogenesis and glycogenolysis after 11 days of high carbohydrate (85% carbohydrate), control (44% carbohydrate), and very low carbohydrate (2% carbohydrate) diets in six healthy men. Diets were eucaloric and provided 15% of energy as protein. Postabsorptive glucose production was measured by infusion of [6,6-2H2]glucose, and fractional gluconeogenesis was measured by ingestion of 2H2O. Postabsorptive glucose production rates were 13.0 +/- 0.7, 11.4 +/- 0.4, and 9.7 +/- 0.4 micromol/kg x min after high carbohydrate, control, and very low carbohydrate diets, respectively (P < 0.001 among the three diets). Gluconeogenesis was about 14% higher after the very low carbohydrate diet (6.3 +/- 0.2 micromol/kg x min; P = 0.001) compared to the control diet, but was not different between the high carbohydrate and control diets (5.5 +/- 0.3 vs. 5.5 +/- 0.2 micromol/kg x min). The rates of glycogenolysis were 7.5 +/- 0.5, 5.9 +/- 0.3, and 3.4 +/- 0.3 micromol/kg x min, respectively (P < 0.001 among the three diets). We conclude that under eucaloric conditions in healthy subjects, dietary carbohydrate content affects the rate of postabsorptive glucose production mainly by modulation of glycogenolysis. In contrast, dietary carbohydrate content affects the postabsorptive rate of gluconeogenesis minimally, as evidenced by only a slight increase in gluconeogenesis during severe carbohydrate restriction.

Adult↗
PubMed1999

Sphingomyelinase treatment of rat hepatocytes inhibits cell-swelling-stimulated glycogen synthesis by causing cell shrinkage.

Breakdown of plasma-membrane sphingomyelin caused by TNF-alpha is known to inhibit glucose metabolism and insulin signalling in muscle and fat cells. In hepatocytes, conversion of glucose to glycogen is strongly activated by amino acid-induced cell swelling. In order to find out whether breakdown of plasma-membrane sphingomyelin also inhibits this insulin-independent process, the effect of addition of sphingomyelinase was studied in rat hepatocytes. Sphingomyelinase (but not ceramide) inhibited glycogen synthesis, caused cell shrinkage, decreased the activity of glycogen synthase a, but had no effect on phosphorylase a. Cell integrity was not affected by sphingomyelinase addition as gluconeogenesis and the intracellular concentration of ATP were unchanged. As a control, glycogen synthesis was studied in HepG2 cells. In these cells, the basal rate of glycogen production was high, could not be stimulated by amino acids, nor be inhibited by sphingomyelinase. Regarding the mechanism responsible for the inhibition of glycogen synthase a, sphingomyelinase did not affect amino acid-induced, PtdIns 3-kinase-dependent, phosphorylation of p70S6 kinase, but caused an increase in intracellular chloride, which is known to inhibit glycogen synthase phosphatase. It is concluded that the decrease in cell volume, following the breakdown of sphingomyelin in the plasma membrane of the hepatocyte, may contribute to the abnormal metabolism of glucose when TNF-alpha levels are high.

Adenosine Triphosphate↗
PubMed1999

Amino acid-dependent signal transduction and insulin sensitivity.

Recent developments indicate that amino acids, in addition to their function as substrates for many metabolic pathways, can stimulate a signal transduction pathway that shares components with insulin-stimulated signalling cascades. Insulin sensitivity is dependent on the ambient amino acid concentration. Amino acid-dependent signal transduction is present in all insulin-sensitive tissues and in pancreatic beta cells. A defect in amino acid-dependent signal transduction may result in phenomena similar to those found in diabetes mellitus.

Amino Acids↗
PubMed1998

Nitric oxide inhibits glycogen synthesis in isolated rat hepatocytes.

There is increasing evidence for the existence of intrahepatic regulation of glucose metabolism by Kupffer cell products. Nitric oxide (NO) is known to inhibit gluconeogenic flux through pyruvate carboxylase and phosphoenolpyruvate carboxykinase. However, NO may also influence glucose metabolism at other levels. Using hepatocytes from fasted rats incubated with the NO-donor S-nitroso-N-acetylpenicillamine, we have now found that the synthesis of glycogen from glucose is even more sensitive to inhibition by NO than gluconeogenesis. Inhibition of glycogen production by NO was accompanied by a rise in intracellular glucose 6-phosphate and UDPglucose. Activity of glycogen synthase, as measured in extracts of hepatocytes after the cells had been exposed to NO, was decreased. Experiments with gel-filtered liver extracts revealed that inhibition of glycogen synthase was caused by an inhibitory effect of NO on the conversion of glycogen synthase b into glycogen synthase a.

Animals↗
PubMed1997

Ala-Pro-cresyl violet, a synthetic fluorogenic substrate for the analysis of kinetic parameters of dipeptidyl peptidase IV (CD26) in individual living rat hepatocytes.

A new type of fluorogenic substrates for proteases based on the leaving group cresyl violet has been synthesized. Cresyl violet is not fluorescent when amino acids or peptide groups are attached but becomes highly fluorescent after proteolytic liberation. Its fluorescence shows linearity with concentration and barely any fading. The properties of Ala-Pro-cresyl violet as substrate for dipeptidyl peptidase IV (DPPIV) (CD26) for localization and quantification of its activity in individual freshly isolated living rat hepatocytes were investigated using confocal microscopy, image analysis, and flow cytometry. DPPIV activity was localized exclusively in patches at plasma membranes likely being bile canalicular domains. Activity was analyzed quantitatively in individual cells by capturing series of images in time. Production of fluorescence was analyzed on the basis of the series of digital images and it appeared to be nonlinear with time. By calculation of the initial velocity at time zero, activity of DPPIV per individual hepatocyte was calculated. Cresyl violet-dependent fluorescence appeared in a similar way when cells were analyzed by flow cytometry. A dipeptide phosphonate inhibitor inhibited production of fluorescence competitively with a Ki of 7 microM. K(m) values in individual hepatocytes varied in the range of 6-22 microM depending on the individual rat from which the hepatocytes were obtained, whereas the Vmax varied in the range of 4-16 nU. K(m) and Vmax values per individual rat were inversely correlated indicating posttranslational regulation of the kinetic parameters of DPPIV. This relationship was lost when membrane fractions of the same hepatocyte suspensions were analyzed. It is concluded that cresyl violet-based protease substrates are the compounds of choice to localize and quantify protease activity in living cells and tissues.

Animals↗
PubMed1997

Cell swelling and glycogen metabolism in hepatocytes from fasted rats.

Cell swelling is known to increase net glycogen production from glucose in hepatocytes from fasted rats by activating glycogen synthase. Since both active glycogen synthase and phosphorylase are present in hepatocytes, suppression of flux through phosphorylase may also contribute to the net increase in glycogen synthesis by cell swelling. We have developed an isotopic procedure to estimate the fluxes through glycogen synthase and phosphorylase in intact hepatocytes and we have examined the effect of cell swelling on both enzyme fluxes. The following observations were made. (1) Hypotonic or glutamine-induced cell swelling increased net glycogen production by activating flux through glycogen synthase with little effect on phosphorylase flux. Proline, previously shown to increase glycogen synthesis more than could be accounted for by its ability to cause cell swelling, increased flux through glycogen synthase and inhibited phosphorylase flux. (2) Incorporation of [14C]glucose into glycogen preceded complete mixing of [14C]glucose with the intracellular pool of UDPglucose. It is concluded that cell swelling affects glycogen synthase only and that UDPglucose is compartmentalized.

Animals↗