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PubMed1992

Synthesis and release of acetylcholine in the rabbit kidney cortex.

Several cholinergic processes were demonstrated and partially characterized in rabbit kidney cortical minces: choline uptake, acetylcholine synthesis and calcium-dependent release. Minces took up labelled choline, acetylated it, and stored it in a pool that was not readily accessible to physostigmine-sensitive cholinesterase activity. [3H]Acetylcholine synthesis but not [3H]choline uptake was inhibited by the removal of sodium ions or incubation at 0 degrees C. The release of newly synthesized [3H]acetylcholine was increased by 300 mOsmol urea in a calcium-dependent manner, but not by potassium depolarization (300 mOsmol), vasopressin (10 microM), or bradykinin (10 microM). These results suggest that acetylcholine may be synthesized by non-neuronal rabbit kidney cortical cells and that this transmitter may be released in response to physiological levels of urea.

Acetylation↗
PubMed1977

[Pathogenesis of the toxic and allergic nephrotic syndrome. Metabolic studies on kidney-cortex slices and on glomeruli].

The in vitro metabolism of isolated rat glomeruli in Daunomycin-nephrosis (DMS) and neophrotoxic nephritis (ANS) was determined in order to investigate questions about the nephrotic syndrome. Glomeruli of rats with Daunomycin-nephrosis influenced metabolic steps as follows: 1. Oxydative decarboxydation of pyruvate and probably also of alpha-ketoglutarate is decreased. This disturbance might be located in the formation of acetyl-and/or succinyl-CoA. 2. Incubation with pyruvate and alpha-ketoglutarat resulted in reduced oxygen uptake, and resynthesis of ATP. 3. Incorporation of thimidin into glomerular DNS is inhibited in the beginning stage of Daunomycin-nephrosis; while incorporation of amino acids into glomerular protein is not, beta-oxydation of fatty acids is at least until entrance into the TCA cycle undisturbed. In contrast, glomeruli of rats with nephrotoxic nephritis utilised more oxygen and the stationary concentration of ATP within the glomeruli was elevated. The pathway of the nephrotic syndrome is not exactly known. Metabolic and morphologic studies with glomeruli of the immunologically and the toxically induced nephrotic syndrome showed different biochemical and histological disorders for the same clinical symptoms. As the beginning of nephrotic syndrome very different lesions in the glomerulus have to be expected, which result in a greater permeability of basal membranes.

Animals↗
PubMed1988

Effect of glycerol on gluconeogenesis in isolated rabbit kidney cortex tubules.

In renal tubules isolated from fed rabbits glycerol is not utilized as a glucose precursor, probably due to the rate-limiting transfer of reducing equivalents from cytosol to mitochondria. Pyruvate and glutamate stimulated an incorporation of [14C]glycerol to glucose by 50- and 10-fold, respectively, indicating that glycerol is utilized as a gluconeogenic substrate under these conditions. Glycerol at concentration of 1.5 mM resulted in an acceleration of both glucose formation and incorporation of [14C]pyruvate and [14C]glutamate into glucose by 2- and 9-fold, respectively, while it decreased the rates of these processes from lactate as a substrate. In the presence of fructose, glycerol decreased the ATP level, limiting the rate of fructose phosphorylation and glucose synthesis. As concluded from the 'cross-over' plots, the ratios of both 3-hydroxybutyrate/acetoacetate and glycerol 3-phosphate/dihydroxyacetone phosphate, as well as from experiments performed with methylene blue and acetoacetate, the stimulatory effect of glycerol on glucose formation from pyruvate and glutamate may result from an acceleration of fluxes through the first steps of gluconeogenesis as well as glyceraldehyde-3-phosphate dehydrogenase. As inhibition by glycerol of gluconeogenesis from lactate is probably due to a marked elevation of the cytosolic NADH/NAD+ ratio resulting in a decline of flux through lactate dehydrogenase.

Acetoacetates↗
PubMed2005

Melatonin-induced modulation of glucose metabolism in primary cultures of rabbit kidney-cortex tubules.

The effect of melatonin on glucose metabolism in the presence and absence of insulin has been investigated in the primary cultures of renal tubules grown in a defined medium. In the absence of glucose in the medium containing 5 microg/mL of insulin and 2 mm alanine + 5 mm glycerol + 0.5 mm octanoate, 100 nm melatonin stimulated both glucose and lactate synthesis, while in the medium devoid of insulin melatonin action was negligible. Melatonin-induced increase in glucose and lactate synthesis was accompanied by an enhancement of alanine and glycerol consumption. In view of measurements of [U-14C]L-alanine and [U-14C]L-glycerol incorporation into glucose, it is likely that melatonin increased alanine utilization for glucose production, while accelerated lactate synthesis was because of an enhanced glycerol consumption. As (i) 10 nm luzindole attenuated the stimulatory action of melatonin on glucose formation and (ii) the indole induced a decrease in intracellular cAMP level, it seems likely that in renal tubules melatonin binds to ML1 membrane receptor subtype. In view of a decline of intracellular fructose-1,6-bisphosphate content accompanied by a significant rise in hexose-6-phosphate and glucose levels, melatonin might result in an acceleration of flux through fructose-1,6-bisphosphatase probably because of an increase in the active, dephosphorylated form of this enzyme. Thus, the administration of melatonin in combination with insulin might be beneficial for diabetic therapy because of protection against hypoglycemia.

Alanine↗
PubMed1976

L-alanine accumulation in isolated tubuli from rat kidney cortex.

Tubuli were prepared from rat renal cortex by modification of the method adopted from HOWARD and PESCH (J.Biol. Chem. 243, 3105, 1968). At 37 degrees C tubuli showed constant pyruvate consumption and glucose production for more than one hour. Intracellular electrolyte and amino acid concentrations were measured after separating the tubuli from the incubation medium by a layer of silicon oil in 5 seconds. During incubation at 37 degrees C L-alanine was accumulated 2.6 fold in the tubuli, while intracellular Na+ concentration dropped to about 50 mEq/l. At 27 degrees C, when pyruvate consumption and glucose production was reduced to less than half compared with 37 degrees C incubation, the respective gradients were higher. L-alanine accumulation was reduced by 2,4-dinitrophenol, antimycin A, ouabain and p-hydroxymercuribenzoate and was completely abolished by the reversal of the Na+ concentration gradient between extracellular and intracellular spaces. At 4 degrees C, when erergy production in tubuli ceased, L-alanine could be concentrated in the case of a Na+o/Na+i ratio greater than unity but not at a lower ratio. It is concluded that the accumulation of L-alanine is a direct function of the energy provided by the Na+ concentration gradient and is mediated by a postulated carrier, which can be injured by sulfhydryl group reagents like p-hydroxymercuribenzoate.

Alanine↗
PubMed1995

Glycerol and lactate induce reciprocal changes in glucose formation and glutamine production in isolated rabbit kidney-cortex tubules incubated with aspartate.

In renal tubules isolated from fed rabbits, 1 mM aspartate is mainly utilized for production of glutamine, glutamate, alanine, and serine, while it is not used for glucose synthesis. However, the addition of either 2 mM glycerol or 2 mM lactate, which are poor gluconeogenic substrates in renal tubules, results in acceleration of both glucose formation and incorporation of [14C]aspartate into glucose by several fold, accompanied by about a twofold decrease in glutamine synthesis and marked accumulation of glutamate and alanine. Ammonium release in renal tubules incubated with aspartate in the presence of methionine sulfoximine, an inhibitor of glutamine synthetase, is also decreased on the addition of glycerol and lactate by about two- and threefold, respectively. Since intracellular [glyceraldehyde 3-phosphate]/[3-phosphoglycerate], [glycerol 3-phosphate]/[dihydroxyacetone phosphate], [lactate]/[pyruvate], and intramitochondrial [glutamate]/[2-oxoglutarate] x [NH4+] ratios are increased in comparison with control values determined with aspartate alone, it is likely that the stimulatory effect of lactate and glycerol on glucose formation from aspartate may be due to (i) an increased availability of reducing equivalents in the cytosol resulting in an enhancement of glyceraldehyde-3-phosphate dehydrogenase activity and (ii) elevation of the mitochondrial NADH/NAD- ratio causing a decrease in glutamate dehydrogenase activity resulting in a diminished glutamine synthesis and enhanced provision of carbon skeleton of aspartate for gluconeogenesis. Stimulation of glucose formation in the presence of 1 mM aspartate + glycerol is not related to cell volume changes. However, an increase for about 30% of intracellular water space induced by 10 mM aspartate + glycerol is accompanied by both diminished gluconeogenesis and enhanced glutamine synthesis, compared with values measured with 1 mM aspartate plus glycerol.

Amino Acids↗
PubMed1994

Complex subcellular distribution of sodium-dependent amino acid transport systems in kidney cortex and LLC-PK1/Cl4 cells.

To characterize the amino acid transport system in basolateral membranes and to test for possible intracellular loci of amino acid transport activity, we surveyed the distribution of L-alanine transport activity in rabbit proximal tubular cells and LLC-PK1/Cl4 cells. A three-dimensional separation procedure based on differential sedimentation, density gradient centrifugation, and counter-current distribution resolved 21 physically and biochemically distinct membrane populations from rabbit cortex. Inhibition of L-alanine transport by phenylalanine and N-(methylamino)isobutyric acid was used to delineate parallel amino acid transport pathways. Population n was identified as brush border membranes by virtue of its 16-fold maltase enrichment; 94% of its Na(+)-dependent alanine transport activity was mediated by systems previously shown to be characteristic of brush border membranes. Two populations, c' and c", which accounted for 25% of the total Na,K-ATPase activity, were identified as basalateral membranes on the basis of Na,K-ATPase cumulative enrichment factors of 15 and 21; 82% of the total alanine transport in these populations was mediated by a Na(+)-independent system similar to the classical system L. Na,K-ATPase, Na(+)-independent and Na(+)-dependent alanine transport activities were associated with intracellular membrane populations as well as with the plasma membranes. The major intracellular locus of Na,K-ATPase activity, population i accounted for roughly 31% of the Na,K-ATPase, maximally enriched ninefold; it contained 29% of the total system L transport activity. Population l, which was identified as endoplasmic reticulum because it was the major locus of membrane-bound NADPH cytochrome c reductase activity, contained 44% of the total system A transport. Three distinct Golgi-derived populations, m', m", and o, accounted for 39% of the total system A transport. A survey of the amino acid transport systems in LLC-PK1/Cl4 cells showed that the majority of system A-mediated amino acid transport was present in membranes of intracellular and possibly apical origin. The presence of large intracellular pools of amino acid transport activities might reflect newly synthesized transport proteins, ongoing membrane recycling or, perhaps, intracellular reserves available for rapid recruitment to the plasma membrane.

Alanine↗
PubMed1993

Carbonic anhydrase II mRNA is induced in rabbit kidney cortex during chronic metabolic acidosis.

Carbonic anhydrase II (CA II), the predominant isoform of carbonic anhydrase in the kidney, is believed to be localized primarily in the cytoplasm of proximal tubule and collecting duct intercalated cells. Carbonic anhydrase facilitates H+ secretion by catalyzing the formation of HCO3- from OH- in the presence of CO2. We have shown that renal cortical CA II activity is stimulated during 4-6 days of chronic metabolic acidosis [L.P. Brion, B.J. Zavilowitz, O. Rosen, and G.J. Schwartz. Am. J. Physiol. 261 (Regulatory Integrative Comp. Physiol. 30): R1204-R1213, 1991]. The purpose of these studies was to examine under similar conditions the regulation of CA II mRNA. We obtained a major portion of the rabbit CA II cDNA by reverse transcription of total RNA from rabbit kidney followed by amplification using oligonucleotide primers prepared from conserved areas in the coding regions of human, mouse, and chick CA II cDNAs in a polymerase chain reaction (RT-PCR). The 696-bp RT-PCR product was sequenced and found to be 71-86% homologous to CA II cDNAs from the other three species. The deduced amino acid sequence agreed closely (> 97%) with a previous Edman analysis of rabbit erythrocyte CA II. Northern analysis showed expression of a approximately 1.4 kb RNA, with cortex > outer medulla > inner medulla. Steady-state mRNA expression from kidney cortex of acid-treated rabbits was about twice that from controls, when normalized to the expression of beta-actin or malate dehydrogenase. The stimulation of CA II mRNA was greater after 3 days than after 5-6 days of acid treatment. (ABSTRACT TRUNCATED AT 250 WORDS)

Alkalosis↗
PubMed1978

Ammoniagenesis in kidney cortex mitochondria of the rat: role of the mitochondrial dicarboxylate anion transporter.

Since glutamine enters rat kidney mitochondria without exchange for an anion, the exit of its carbon skeleton must involve the dicarboxylate anion transporter (malate - inorganic phosphate) for ammoniagenesis to proceed. Therefore, this important mitochondrial anion transporter was studied in isolated renal cortex mitochondria. The phosphate concentration required for half-maximal rates of malate exit from renal mitochondria of normal rats was 1.0 mM. This value was not decreased in renal cortex mitochondria from rats with chronic metabolic acidosis. The maximum velocity of the dicarboxylate transporter was not increased in renal cortex mitochondria from these acidotic rats. These kinetic parameters were similar in liver mitochondria. There was no acute activation of the dicarboxylate carrier when the incubation medium pH lowered. Thus, there is no demonstrable activation of the dicarboxylate anion transporter in kidney cortex mitochondria of the rat with chronic metabolic acidosis. The significance of these results with respect to the regulation of renal ammoniagenesis is discussed.

Acidosis↗
PubMed1979

Uptake of glycine by human kidney cortex.

The transport of glycine was investigated in histologically normal adult human kidney cortical slices. Uptake occurs against a gradient and shows concentration dependence. Kinetic analysis reveals two systems for transport of glycine with apparent transport Km values of 0.511 and 34.2 mM. Glycine transport on the high-Km system is competitively inhibited by 50 mML-proline. Transport inhibition on the low-Km system could not be directly evaluated, but on theoretic grounds appears not to be inhibited by L-proline or hydroxyproline. Alpha-aminoisobutyric acid, valine, and thioproline are also shown to inhibit glycine uptake. Low medium sodium or anaerobic incubation depress the uptake of glycine. These observations are consistent with previous reports of glycine transport in rat kidney and support the proposals for the mechanism of familial iminoglycinuria based on in vivo investigations.

Adult↗
PubMedDate not supplied

[Effect of hypokinesia on the intensity of gluconeogenesis in the rat kidney cortex].

The rate of gluconeogenesis was measured in the cortical layer of kidneys of 95 white rats on hypokinesia days 1, 3, 7, 15, 30 and 60. At early stages of hypokinesia the rate of glucose formation from aspartic, glutamic, pyruvic, alpha-ketoglutaric acids and glycerol increased, specifically on hypokinesia day 3. The rate of glucose formation from the amino acids on hypokinesia day 30 was identical to that in the controls. The rate of glucose formation from alpha-ketoglutaric and succinic acids increased and that from pyruvic acid significantly decreased. On hypokinesia day 30 the rate of glucose formation from every substrate used, except for pyruvic acid, increased. The glucose concentration in serum was higher on hypokinesia days 1-7 and lower on hypokinesia days 15-60. The changes in the rate of glucose formation in the kidneys make inexplicable stable hypoglycemia seen at later stages of hypokinesia.

Animals↗