Effect of valproate on lactate and glutamine metabolism by rat renal cortical tubules

The metabolic effects of sodium valproate (VPA) on rat renal cortical tubules have been examined. When 1 or 5 mM lactate was used as substrate in the incubation medium, VPA decreased markedly the lactate uptake by the tubules. When 1 or 5 mM glutamine was used, the addition of VPA accelerated glutamine uptake, ammoniagenesis, but also stimulated markedly the accumulation of lactate and pyruvate produced from glutamine. VPA had a dose-dependent inhibitory effect on gluconeogenesis from both glutamine and lactate. With 5 mM glutamine, VPA also induced a significant accumulation of glutamate in the medium. The oxygen consumption by the tubules was diminished by 40% following VPA addition. It is concluded that VPA modifies the metabolism of rat cortical tubules by interfering with the oxidation of natural substrates and stimulates in this fashion the production of ammonia by kidney tubules.     

Metabolic fate of glutamate carbon in rat renal tubules. Studies with 13C nuclear magnetic resonance and gas chromatography-mass spectrometry.

13C-n.m.r. spectroscopy and g.c.-m.s. were used to determine the metabolic fate of glutamate carbon in rat kidney. The main purpose was to characterize the effect of chronic metabolic acidosis on the utilization of glutamate carbon. Renal tubules obtained from normal and chronically acidotic rats were incubated in Krebs buffer, pH 7.4, in the presence of 2.5 mM-[3-13C]glutamate. During the course of incubation the concentrations of total glucose and NH3 were significantly (P less than 0.05) higher in tissue from acidotic rats. The levels of some tricarboxylic-acid-cycle intermediates were higher (P less than 0.05) in control tissue. In control tissue, 13C-n.m.r. spectra demonstrated a significantly higher rate of 13C appearance of aspartate, glutamine and [2,4-13C]glutamate. However, in acidosis the resonances of [13C]glucose carbon atoms were significantly higher. In the control, approx. 15% of glutamate carbon was accounted for by [13C]glucose formation as against 30% in chronic acidosis. However, in control tissue, 44% of glutamate carbon utilization was accounted for by recycling to glutamate and formation of aspartate, glutamine and GABA. In acidosis, only 11% was so recovered. Analysis of 15NH3 formation during the course of incubation with 2.5 mM-[15N]glutamate demonstrated a positive association between the appearance of [13C]glucose and 15NH3 both in the control and in acidosis. The data suggest that the control of gluconeogenesis and ammoniagenesis in acidosis is, in part, referable to a diminution in the rate of the reductive amination of alpha-oxoglutarate, that of the transamination reaction and that of glutamine synthesis.     

Inhibition of glutamine synthetase in the mouse kidney: a novel mechanism of adaptation to metabolic acidosis

As part of a study on the regulation of renal ammoniagenesis in the mouse kidney, we investigated the effect of chronic metabolic acidosis on glutamine synthesis by isolated mouse renal proximal tubules. The results obtained reveal that, in tubules from control mice, glutamine synthesis occurred at high rates from glutamate and proline and, to a lesser extent, from ornithine, alanine, and aspartate. A 48 h, metabolic acidosis caused a marked inhibition of glutamine synthesis from near-physiological concentrations of both alanine and proline that were avidly metabolized by the tubules; metabolic acidosis also greatly stimulated glutamine utilization and metabolism. These effects were accompanied by a large increase (i) in alanine, proline, and glutamine gluconeogenesis and (ii) in ammonia accumulation from proline and glutamine. In the renal cortex of acidotic mice, the activity of phosphoenolpyruvate carboxykinase increased 4-fold, but that of glutamate dehydrogenase did not change; in contrast with what is known in the rat renal cortex, metabolic acidosis markedly diminished the glutamine synthetase activity and protein level, but not the glutamine synthetase mRNA level in the mouse renal cortex. These results strongly suggest that, in the mouse kidney, glutamine synthetase is an important regulatory component of the availability of the ammonium ions to be excreted for defending systemic acid-base balance. Furthermore, they show that, in rodents, the regulation of renal glutamine synthetase is species-specific.     

Metabolic effects of valproate on dog renal cortical tubules

The effect of valproate (0.01-10 mM), an antiepileptic drug inducing hyperammonemia in humans, was studied in vitro on a suspension of renal cortical tubules (greater than 85% proximal tubules) obtained from six normal dogs. When these tubules were incubated with 1 mM glutamine, the addition of valproate accelerated glutamine uptake, ammoniagenesis, and the production of alanine, lactate, and pyruvate. With 5 mM glutamine, a rise in glutamate accumulation, a much greater synthesis of alanine, an important aspartate production, and a striking accumulation of lactate and pyruvate were observed. With 1 or 5 mM lactate, lactate utilization and gluconeogenesis were markedly reduced with increasing concentrations of valproate. Oxygen consumption was reduced by only 15-20% by 10 mM valproate. The accelerated glutamine utilization resulting from valproate could not be prevented by aminooxyacetate, an inhibitor of transamination. Valproate also reduced various enzymatic activities, a finding that could not explain its metabolic effects. Four sites of action may explain these various metabolic changes: (i) a stimulation of mitochondrial glutamine transport, (ii) an increase in the flux of glutamate to malate, and (iii) a reduction in the net oxidation of pyruvate and (iv) in the flux through pyruvate carboxylase.     

Concomitant synthesis and degradation of glutamine in isolated rabbit kidney tubules

When rabbit kidney tubules were incubated with 1 mM [1-14C]glutamine as substrate, a release of 14CO2 together with a net production of glutamine were observed. That glutamine utilization was masked by higher rates of concomitant glutamine synthesis was demonstrated by: (i) inhibiting glutamine synthesis; and (ii) measuring the specific radioactivity of [1-14C]glutamine which fell during incubation.     

Uptake and metabolism of glutamine in cultured kidney cells

The metabolism of glutamine was investigated in cultured rat kidney cells. Glutamine utilization and product formation were followed as a function of time at either 10 microM or 1 mM initial glutamine concentration. At 1 mM glutamine, glutamate and gamma-glutamylglutamate were the major products formed at the end of a 5-min incubation period; glutamate accounted for 46% while gamma-glutamylglutamate accounted for 33% of the glutamine utilized. With time, glutamate continued to accumulate while gamma-glutamyl peptide formation leveled off. The role of gamma-glutamyl transpeptidase was assessed by using hippurate, a physiological activator of gamma-glutamyl transpeptidase and acivicin, L-(alpha S,5S)-alpha-amino-3-chloro-4,5-dihydro-5-isoxazoleacetic acid, an inhibitor of gamma-glutamyl transpeptidase. Hippurate, 4 mM, increased the utilization of glutamine and the formation of glutamate, gamma-glutamyl peptides and ammonia. Exposure of cells to acivicin resulted in 98% inhibition of gamma-glutamyl transpeptidase without effecting phosphate-dependent glutaminase activity. Acivicin inhibition resulted in a decreased utilization of glutamine and product formation as compared to control; 5-oxoproline appearance fell 70%. The fractional distribution of glutamine carbon and nitrogen into its metabolic products in control, hippurate and acivicin-treated cells showed no change at the end of 60 min. The data provide evidence that gamma-glutamyl transpeptidase utilizes glutamine and forms gamma-glutamyl peptides in cultured kidney cells.     

Organic mercurial diuresis: inhibition of glutamine utilization in the acidotic rat.

Organic mercurials inhibit mitochondrial glutamine metabolism in vitro while metabolic acidosis, a condition in which the predominant renal fuel is glutamine, potentiates mercurial diuresis. The following studies were undertaken to determine whether potentiation of diuresis reflects mercurial inhibition of glutamine utilization. (1) All three mercurials employed (mersalyl, chlormerodrin, and p-chloromercuribenzoate) are diuretics in the rat and this effect was potentiated by NH4Cl. (2) Despite reabsorbing less sodium, mercurial-treated rats had lower kidney ATP content (4.35 +/- 0.26 and 3.84 +/- 0.43 mumol/g dry weight (mercurial plus NH4Cl) than did controls (4.95 +/- 0.31 and 4.87 +/- 0.39 mumol/g dry weight (NH4Cl). (3) Isolated kidneys from NH4Cl and NH4Cl plus mercurial treated rats were perfused with 1 mM L-[U-14C]glutamine to determine rates of extraction and oxidation. Mercurial-treated acidotic rat kidneys had a reduced rate of glutamine uptake (40.8 +/- 7.4 vs. 64.8 +/- 5.8 mumol/h per kidney), a diminished rate of glutamine conversion to CO2 (14.8 +/- 3.6 vs. 26.4 +/- 5.2 mumol/h per kidney), and a reduction in glucose production (16 +/- 5 vs. 27 +/- 4 mumol/h per kidney). These results are consistent with an effect of organic mercurials upon glutamine utilization, limiting ATP availability, and thereby reducing tubular active sodium reabsorption.     

Contribution of pH-sensitive metabolic processes to pH homeostasis in isolated rat kidney tubules

The metabolism of isolated rat kidney tubules suspended in calcium-free physiological saline buffered with phosphate was found to be sensitive to changes in the pH of the suspending medium. Lowering the pH from 7.8 to 6.4 brought about increases in the rates of oxidation of added succinate, glutamate or glutamine as well as in the production of glucose from lactate, glutamine, succinate and fructose. The cellular ATP level was also higher in tubules incubated at pH 6.4. In contrast, the utilization of added glucose was greater at pH 7.8 than at pH 6.4, a substantial amount of lactate being produced at the higher pH. When glucose and either lactate or glutamine were provided as co-substrates glucose was the preferred fuel at pH 7.8 but the alternative substrate was the more readily utilized at pH 6.4. As a consequence of the metabolic activities of the tubules the pH of the suspending medium changed, utilization of lactate, glutamate or glutamine causing a rise in pH while conversion of glucose to lactate caused a fall in pH. In cases where two substrates were metabolized concurrently over a period of 3 h the extracellular pH tended towards a plateau level of approximately pH 7.4. It is proposed that pH-sensitive metabolism in isolated kidney tubules contributes to pH homeostasis in the cellular environment.     

Contribution of pH-sensitive metabolic processes to pH homeostasis in isolated rat kidney tubules.

The metabolism of isolated rat kidney tubules suspended in calcium-free physiological saline buffered with phosphate was found to be sensitive to changes in the pH of the suspending medium. Lowering the pH from 7.8 to 6.4 brought about increases in the rates of oxidation of added succinate, glutamate or glutamine as well as in the production of glucose from lactate, glutamine, succinate and fructose. The cellular ATP level was also higher in tubules incubated at pH 6.4 In contrast, the utilization of added glucose was greater at pH 7.8 than at pH 6.4, a substantial amount of lactate being produced at the higher pH. When glucose and either lactate or glutamine were provided as co-substrates glucose was the preferred fuel at pH 7.8 but the alternative substrate was the more readily utilized at pH 6.4. As a consequence of the metabolic activities of the tubules the pH of the suspending medium changed, utilization of lactate, glutamate or glutamine causing a rise in pH while conversion of glucose to lactate caused a fall in pH. In cases where two substrates were metabolized concurrently over a period of 3 h the extracellular pH tended towards a plateau level of approximately pH 7.4. It is proposed that pH-sensitive metabolism in isolated kidney tubules contributes to pH homeostasis in the cellular environment.     

Metabolism of glutamine and glutamate by rat renal tubules. Study with 15N and gas chromatography-mass spectrometry

Gas chromatography-mass spectrometry was utilized to study the metabolism of [15N]glutamate, [2-15N]glutamine, and [5-15N]glutamine in isolated renal tubules prepared from control and chronically acidotic rats. The main purpose was to determine the nitrogen sources utilized by the kidney in various acid-base states for ammoniagenesis. Incubations were performed in the presence of 2.5 mM 15N-labeled glutamine or glutamate. Experiments with [5-15N]glutamine showed that in control animals approximately 90% of ammonia nitrogen was derived from 5-N of glutamine versus 60% in renal tubules from acidotic rats. Experiments with [2-15N]glutamine or [15N]glutamate indicated that in chronic acidosis approximately 30% of ammonia nitrogen was derived either from 2-N of glutamine or glutamate-N by the activity of glutamate dehydrogenase. Flux through glutamate dehydrogenase was 6-fold higher in chronic acidosis versus control. No 15NH3 could be detected in renal tubules from control rats when [2-15N]glutamine was the substrate. The rates of 15N transfer to other amino acids and to the 6-amino groups of the adenine nucleotides were significantly higher in normal renal tubules versus those from chronically acidotic rats. In tubules from chronically acidotic rats, 15N abundance in 15NH3 and the rate of 15NH3 appearance were significantly higher than that of either the 6-amino group of adenine nucleotides or the 15N-amino acids studied. The data indicate that glutamate dehydrogenase activity rather than glutamate transamination is primarily responsible for augmented ammoniagenesis in chronic acidosis. The contribution of the purine nucleotide cycle to ammonia formation appears to be unimportant in renal tubules from chronically acidotic rats.     

Brain glutamate metabolism during metabolic alkalosis and acidosis.

Glutamate modifies ventilation by altering neural excitability centrally. Metabolic acid-base perturbations may also alter cerebral glutamate metabolism locally and thus affect ventilation. Therefore, the effect of metabolic acid-base perturbations on central nervous system glutamate metabolism was studied in pentobarbital-anesthetized dogs under normal acid-base conditions and during isocapnic metabolic alkalosis and acidosis. Cerebrospinal fluid transfer rates of radiotracer [13N]ammonia and of [13N]glutamine synthesized de novo via the reaction glutamate+NH3-->glutamine in brain glia were measured during normal acid-base conditions and after 90 min of acute isocapnic metabolic alkalosis and acidosis. Cerebrospinal fluid [13N]ammonia and [13N]glutamine transfer rates decreased in metabolic acidosis. Maximal glial glutamine efflux rate jm equals 85.6 +/- 9.5 (SE) mumol.l-1 x min-1 in all animals. No difference in jm was observed in metabolic alkalosis or acidosis. Mean cerebral cortical glutamate concentration was significantly lower in acidosis [7.01 +/- 0.45 (SE) mumol/g brain tissue] and tended to be larger in alkalosis, compared with 7.97 +/- 0.89 mumol/g in normal acid-base conditions. There was a similar change in cerebral cortical gamma-aminobutyric acid concentration. Within the limits of the present method and measurements, the results suggest that acute metabolic acidosis but not alkalosis reduces glial glutamine efflux, corresponding to changes in cerebral cortical glutamate metabolism. These results suggest that glutamatergic mechanisms may contribute to central respiratory control in metabolic acidosis.     

Influence of dietary energy intake and substrate addition on the in vitro metabolism of glucose and glutamine in rumen epithelial tissue

Ten Holstein steers were fed either 14.2 or 26.2 Mcal ME for 28 days prior to investigating the effect of dietary energy on epithelial metabolism. Rumen papillae were incubated in vitro with glucose (5 mM) or glutamine (1 mM) as well as additional energy substrates. Increased dietary intake increased production of 14CO2 from glucose and glutamine, increased uptake and net lactate production from glucose, and decreased net glutamate and alanine production from glutamine. At these substrate concentrations, rates of glucose oxidation to 14CO2 were sevenfold higher than glutamine.     

The transport and metabolism of glutamine by kidney-cortex mitochondria from normal and acidotic rats.

1. The oxidation of glutamine by kidney-cortex mitochondria from normal and acidotic rats was not inhibited by avenaciolide, which did inhibit glutamate uptake and oxidation. The oxidation of glutamine by these mitochondria was always greater than that of glutamate. Direct measurements of the metabolism of [1-14C]glutamine in the presence of glutamate, and of [1-14C]glutamate in the presence of glutamine, demonstrated that the uptake and metabolism of external glutamate is insufficient to account for the observed rate of glutamine uptake and metabolism. Thus the postulated glutamine/glutamate antiport does not play a quantitatively important role in the metabolism of glutamine by renal mitochondria. 2. Rapid swelling of these mitochondria was observed in iso-osmotic solutions of L-glutamine and L-glutamyl-gamma-monohydroxamate but not in D-glutamine or L-isoglutamine (1-amido-2-aminoglutaric acid). Thus a relatively specific glutamine uniport exists in these mitochondria. 3. The utilization of glutamine was increased about 3-fold in mitochondria from chronically acidotic rats. Thus mitochondrial adaptations play an important part in the renal response to metabolic acidosis.     

Fate of intraluminal glutamine in the perfused renal tubule

To determine the fate of intraluminal glutamine and specifically the role of brush border gamma glutamyltransferase in its hydrolysis and reabsorption, proximal convoluted tubules of rabbits were isolated and perfused with an artificial ultrafiltrate containing 1 mM 14C-glutamine and 3H-PEG as a volume absorption marker. The tubules, average length 0.80 +/- 0.09 mm, were bathed in perfusate containing albumin, 6.5 percent but no glutamine. Aliquots of collectate and bathing media were monitored for total 14C counts while the distribution of radioactive 14C between glutamine and glutamate in the collectate was determined by separation on a Dowex X8 formate form ion-exchange column. After 3 ten minute control periods the perfusate was switched to one containing 1 mM AT-125 in addition to glutamine and after equilibration an additional 3 collections were obtained. Control period glutamine load averaged 16.1 +/- 2.4 pmole/min of which 35 percent was absorbed and 38 and 27 percent excreted as glutamine and glutamate respectively; of the absorbed glutamine 25 percent was metabolized. During AT-125 administration, glutamine delivery averaged 15.0 +/- 2.1 pmole/min of which 57 percent was absorbed; increased absorption occurred at the expence of intraluminal glutamate formation which fell to less than 10 percent. Thus luminal transport and gamma glutamyltransferase mediated hydrolysis appear to compete for available glutamine. Significantly, reducing intraluminal glutamine hydrolysis doubles the cellular metabolism of absorbed glutamine suggesting that extracellular conversion of glutamine to glutamate alters the metabolic fate of filtered glutamine.     

Metabolic Fate of 14C-Labeled Glutamate in Astrocytes in Primary Cultures

The metabolic fate of L-[U-14C]- and L-[1-14C]glutamate was studied in primary cultures of mouse astrocytes. Conversion of the uniformly labeled compound to glutamine and aspartate was followed by determination of specific activities after dansylation with [3H]dansyl chloride and subsequent thin layer chromatography of the dansylated amino acids. Metabolic fluxes were calculated from the alterations of specific activities and the pool sizes, which were likewise measured by a dansylation method. Formation of 14CO2 from [1-14C]glutamate was determined by the trapping of CO2 in hyamine hydroxide in a gas-tight chamber, which is, in the known absence of glutamate decarboxylase activity in the cultured astrocytes, an unequivocal expression of the metabolic flux via alpha-ketoglutarate to CO2 and succinyl-CoA. The metabolic fluxes determined by these procedures amounted to 2.4 nmol/min/mg protein for glutamine synthesis, 1.1 nmol/min/mg protein for aspartate production, and 4.1 nmol/min/mg protein for formation and subsequent decarboxylation of alpha-ketoglutarate. The latter process was unaffected by virtually complete inhibition of glutamate-oxaloacetic transaminase with aminooxyacetic acid, indicating that the formation of alpha-ketoglutarate occurs as an oxidative deamination rather than as a transamination. This suggests that the formation of alpha-ketoglutarate from glutamate represents a net degradation, not an isotopic exchange.     

Calcium-ion transport by intact synaptosomes. Intrasynaptosomal compartmentation and the role of the mitochondrial membrane potential.

1. The pathways and the fate of glutamate carbon and nitrogen were investigated in isolated guinea-pig kidney-cortex tubules. 2. At low glutamate concentration (1 mM), the glutamate carbon skeleton was either completely oxidized or converted into glutamine. At high glutamate concentration (5 mM), glucose, lactate and alanine were additional products of glutamate metabolism. 3. At neither concentration of glutamate was there accumulation of ammonia. 4. Nitrogen-balance calculations and the release of 14CO2 from L-[1-14C]glutamate (which gives an estimation of the flux of glutamate carbon skeleton through alpha-oxoglutarate dehydrogenase) clearly indicated that, despite the absence of ammonia accumulation, glutamate metabolism was initiated by the action of glutamate dehydrogenase and not by transamination reactions as suggested by Klahr, Schoolwerth & Bourgoignie [(1972) Am. J. Physiol. 222, 813-820] and Preuss [(1972) Am. J. Physiol. 222, 1395-1397]. Additional evidence for this was obtained by the use of (i) amino-oxyacetate, an inhibitor of transaminases, which did not decrease glutamate removal, or (ii) L-methionine DL-sulphoximine, an inhibitor of glutamine synthetase, which caused an accumulation of ammonia from glutamate. 5. Addition of NH4Cl plus glutamate caused an increase in both glutamate removal and glutamine synthesis, demonstrating that the supply of ammonia via glutamate dehydrogenase is the rate-limiting step in glutamine formation from glutamate. NH4Cl also inhibited the flux of glutamate through glutamate dehydrogenase and the formation of glucose, alanine and lactate. 6. The activities of enzymes possibly involved in the glutamate conversion into pyruvate were measured in guinea-pig renal cortex. 7. Renal arteriovenous-difference measurements revealed that in vivo the guinea-pig kidney adds glutamine and alanine to the circulating blood.     

Increased activity of renal glycine-cleavage-enzyme complex in metabolic acidosis.

Glycine is metabolized in isolated renal cortical tubules to stochiometric qualities of ammonia, CO2 and serine by the combined actions of the glycine-cleavage-enzyme complex and serine hydroxymethyltransferase. The rate of renal glycine metabolism by this route is increased in tubules from acidotic rats, but is not affected in vitro by decreasing the incubation pH from 7.4 to 7.1. Metabolic acidosis caused an increase in the renal activity of the glycine-cleavage-enzyme complex, but there were no changes in the activity of serine hydroxymethyltransferase or of methylenetetrahydrofolate dehydrogenase. This enzymic adaptation permits increased ammoniagenesis from glycine during acidosis. The physiological implications are discussed.     

Glutamate Metabolism in Rat Cortical Astrocyte Cultures

Glutamate metabolism in rat cortical astrocyte cultures was studied to evaluate the relative rates of flux of glutamate carbon through oxidative pathways and through glutamine synthetase (GS). Rates of 14CO2 production from [1-14C]glutamate were determined, as was the metabolic fate of [14C(U)]glutamate in the presence and absence of the transaminase inhibitor aminooxyacetic acid and of methionine sulfoximine, an irreversible inhibitor of GS. The effects of subculturing and dibutyryl cyclic AMP treatment of astrocytes on these parameters were also examined. The vast majority of exogenously added glutamate was converted to glutamine and exported into the extracellular medium. Inhibition of GS led to a sustained and greatly elevated intracellular glutamate level, thereby demonstrating the predominance of this pathway in the astrocytic metabolism of glutamate. Nevertheless, there was some glutamate oxidation in the astrocyte culture, as evidenced by aspartate production and labeling of intracellular aspartate pools. Inhibition of aspartate aminotransferase caused a greater than 70% decrease in 14CO2 production from [1-14C]glutamate. Inhibition of GS caused an increase in aspartate production. It is concluded that transamination of glutamate rather than oxidative deamination catalyzed by glutamate dehydrogenase is the first step in the entry of glutamate carbon into the citric acid cycle in cultured astrocytes. This scheme of glutamate metabolism was not qualitatively altered by subculturing or by treatment of the cultures with dibutyryl cyclic AMP.     

Glutamine and glucose metabolism in bovine blood lymphocytes.

1. Glutamine and glucose metabolism was studied in bovine blood lymphocytes incubated at 37 degrees C in the presence of Krebs-Ringer bicarbonate buffer (pH 7.4) containing 1 mM [U-14C]glutamine and 5 mM [U-14C]glucose, respectively. 2. The major metabolic products from glutamine were ammonia, glutamate, and to a lesser extent, aspartate and CO2. Glucose was metabolized mainly to lactate and, to a lesser extent, pyruvate and CO2. These findings indicate incomplete oxidation of glutamine and glucose carbons in bovine blood lymphocytes. 3. Glucose provided three-fold greater amounts of energy to bovine blood lymphocytes than did glutamine on the basis of their measured end-products. Glycolysis accounted for 50% of glucose-derived ATP production. 4. Our findings suggest similar metabolic patterns of glutamine and glucose in lymphocytes between ruminants and non-ruminant species (e.g. rats). However, in contrast to rat peripheral lymphocytes, glucose, rather than glutamine, was a major energy substrate for bovine blood lymphocytes.     

Acidosis and astrocyte amino acid metabolism

The relationship between acidosis and the metabolism of glutamine and glutamate was studied in cultured astrocytes. Acidification of the incubation medium was associated with an increased formation of aspartate from glutamate and glutamine. The rise of the intracellular content of aspartate was accompanied by a significant decline in the extracellular concentration of both lactate and citrate. Studies with either [2-(15)N]glutamine or [15N]glutamate indicated that there occurred in acidosis an increased transamination of glutamate to aspartate. Studies with L-[2,3,3,4,4-(2)H5]glutamine indicated that in acidosis glutamate carbon was more rapidly converted to aspartate via the tricarboxylic acid cycle. Acidosis appears to result in increased availability of oxaloacetate to the aspartate aminotransferase reaction and, consequently, increased transamination of glutamate. The expansion of the available pool of oxaloacetate probably reflects a combination of: (a) Restricted flux through glycolysis and less production from pyruvate of acetyl-CoA, which condenses with oxaloacetate in the citrate synthetase reaction; and (b) Increased oxidation of glutamate and glutamine through a portion of the tricarboxylic acid cycle and enhanced production of oxaloacetate from glutamate and glutamine carbon. The data point to the interplay of the metabolism of glucose and that of glutamate in these cells.