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PubMed1977

Regulation of citrate transport and pyruvate dehydrogenase in rat kidney cortex mitochondria by bicarbonate.

1. Bicarbonate increased citrate and 2-oxoglutarate accumulation when rat kidney cortex mitochondria were incubated with pyruvate or L(-)-palmitoyl carnitine in the presence of L-malate. 2. Bicarbonate stimulated the exit of citrate from mitochondria. The Km for bicarbonate was 13.5 mM and the Vmax was 0.59 nmol/min/mg of protein at 10 degrees. 3. The bicarbonate-stimulated exit of citrate from the mitochondria was prevented by inhibitors of the tricarboxylate, dicarboxylate, and phosphate transport systems. 4. The activity of pyruvate dehydrogenase was significantly increased by preincubation of rat kidney mitochondria with bicarbonate. This bicarbonate-induced activation was not observed in presence of inhibitors of citrate transport. Bicarbonate did not activate pyruvate dehydrogenase in rat heart mitochondria. Bicarbonate had no effect on pyruvate dehydrogenase activity in either broken mitochondria or whole tissue preparations. 5. The mechanism of this activation is discussed in the light of the known regulatory properties of pyruvate dehydrogenase, pyruvate carboxylase, and citrate synthase.

Animals↗
PubMed1983

A high-affinity, calmodulin-dependent Ca2+ pump in the basal-lateral plasma membranes of kidney cortex.

A purified preparation of kidney basolateral membrane vesicles is capable of ATP-dependent Ca2+ uptake. The reaction has high affinity for Ca2+ (Km about 0.1 microM) and a V of 5.8 nmol Ca2+ X mg-1 protein X min-1 in the predominantly right-side-out vesicular preparation used. It is inhibited by vanadate (K0.5 about 5 microM) and by anti-calmodulin drugs. A stimulatory effect of calmodulin is visible in membranes depleted of the activator. Exposure of basolateral membranes to 125I-azido-modified calmodulin results in the specific labeling of a membrane protein of Mr 141 000, which is tentatively suggested to be the Ca2+-pumping ATPase.

Adenosine Triphosphate↗
PubMed1977

Studies on the pathogenesis of ischemic cell injury. VI. Accumulation of calcium by isolated mitochondria of ischemic rat kidney cortex.

Mitochondria isolated from rat kidney subject to in vitro ischemia at various time intervals demonstrated a continuous decline of the ability to accumulate calcium following a high initial stable phase of accumulation of calcium which is dependent both on ATP and respiration. This decline occurs during the reversible phase of cell injury and appears to be a sensitive indicator of membrane changes in a binding and/or transport protein or of other membrane permeability characteristics. The morphology of mitochondrial densities related to calcium accumulation in mitochondria varied. Any form of calcium accumulation, resulted in marked swelling of mitochondria. Control renal mitochondria in sucrose were highly condensed. Partially inhibited calcium accumulation in the presence of phosphate was also associated with numerous small spheric or punctate deposits in close relationship to the inner membrane. Uninhibited calcium accumulation resulted in the formation of needle-like structures radiating from such inner membrane associated sites.

Adenosine Triphosphate↗
PubMed1993

Purification and characterization of an alkaline proteinase from kidney cortex lysosomes.

An alkaline proteinase was purified to apparent homogeneity from buffalo (Bubalus bubalis) kidney cortex lysosomes by affinity chromatography on STI sepharose 4B and gel filtration over Sephadex G-100. The molecular weight of the enzyme was 17,000 and 21,000 by gel filtration and SDS/PAGE respectively. The purified enzyme was optimally active at pH 8.5-9.0 at 50 degrees C and hydrolysed synthetic substrates of chymotrypsin but not those of elastase or trypsin. It was inhibited by serine proteinase inhibitors like soybean trypsin inhibitor, limabean trypsin inhibitor and phenylmethyl sulphonyl fluoride. Immunologically, the enzyme was similar to chymotrypsin. The amino acid composition showed high content of acidic amino acids. This protein was detected in kidney, liver, spleen, pancreas and heart.

Amino Acid Sequence↗
PubMedDate not supplied

[Native and desensitized forms of L-type pyruvate kinase from rabbit kidney cortex].

A time-consuming procedure of isolation of pyruvate kinase isoenzymes from rabbit kidney cortex (more than 5 hrs) at 0-2 degrees led to obtaining of a desensitized form of "L" type, resembling the "M3" type of the enzyme from sceletal muscle. Rapid isolation of pyruvate kinase "L" type (within about 2.5 hrs) at 4-6 degrees provided the isoenzyme in the active (allosteric) form.

Allosteric Site↗
PubMed1966

The fate of isotopic carbon in kidney cortex synthesizing glucose from lactate.

1. When slices of kidney cortex are incubated with lactate and acetoacetate, lactate is almost quantitatively converted into glucose whereas acetoacetate provides a major part of the fuel of respiration. 2. In apparent contrast with these findings a large fraction of (14)C-labelled acetoacetate appears in glucose and a large fraction of (14)C-labelled lactate appears in the carbon dioxide. 3. The findings can be explained by: (a) the participation of oxaloacetate as an intermediate of both gluconeogenesis and respiration; (b) the fact that the carbon dioxide formed in the course of one turn of the tricarboxylic acid cycle is exclusively derived from oxaloacetate. 4. As a result there is a ;crossing over' of the carbon of the substrate of respiration to the pathway of gluconeogenesis and of the carbon of the glucogenic precursors to the pathway of respiration. 5. In the given situation the fate of the label does not allow predictions to be made about the net fate of the labelled metabolites. 6. The implications of the findings on the interpretation of isotopic data are discussed.

Acetoacetates↗
PubMed1985

Interaction of cadmium, zinc and copper in relation to smoking habit, age and histopathological findings in human kidney cortex.

In this study the concentrations of cadmium, zinc and copper were determined by atomic absorption spectrophotometry in 51 post mortem kidney cortex samples. A histopathological examination of the kidney was also performed. These parameters, together with age and smoking habit, were statistically related by means of factor analysis. The results show that the first factor associated smoking habit, cadmium and zinc and the second factor histopathological findings and age.

Age Factors↗
PubMedDate not supplied

[Effect of Ca2+ ions on the pyruvate kinase isoenzymes from rabbit kidney cortex].

Ca2 ions showed the various effect on isoenzymes of pyruvate kinase from rabbit kidney cortex. Ca2 activated the "L" type of pyruvate kinase at low concentrations of PEP and inhibited -- at high concentrations of the latter. "M2" type of pyruvate kinase was inhibited by Ca2 under all the conditions studied. In presence of Ca2+ the activating effect of PDP on "L" and "M2" types of pyruvate kinase was absent; the inhibitory action of ATP on the "M" type of pyruvate kinase was increased at all the concentrations above 1.3 mM. The effect of Ca2+ on the pyruvate kinase isoenzymes depended on content of Mg2+ in the medium.

Adenosine Triphosphate↗
PubMed1989

Isolation and characterization of dipeptidyl aminopeptidase IV from human kidney cortex.

Intact dipeptidyl aminopeptidase IV (DAP IV) was solubilized by bromelain treatment from human kidney brush border plasma-membranes. Purification of DAP IV was performed by a 3-step method, applying lectin-affinity chromatography on WGA-Sepharose, gel filtration and anion-exchange chromatography. DAP IV from human kidney cortex showed a pH optimum of 8.7 and was totally inhibited by 1 mmol/l Zn2+. Isolated DAP IV revealed a relative molecular mass of 250 kDa as determined by the native-PAGE method and of 220 kDa by the gel filtration method. Analytical isoelectric focussing of DAP IV revealed an isoelectric point of pH 5.3. Ultrastructural analysis of isolated DAP IV fractions, using the negative staining technique, disclosed the presence of numerous globular particles with an average diameter of 5 nm which correspond to the structural substrate of the purified protein.

Dipeptidyl Peptidase 4↗
PubMed1991

Increased Na pump activity in the kidney cortex of the Milan hypertensive rat strain.

The (Na+,K+)-ATPase activity from the kidney cortex of the Milan hypertensive rat strain (MHS) and the corresponding normotensive control (MNS) was measured both in active solubilized enzyme preparations and in isolated basolateral membrane vesicles. Kinetic analysis of the purified enzyme showed that the Vmax value was significantly higher in MHS rats. The difference between MHS and MNS was not linked to a different number of sodium pumps, but was related to the molecular activity of the enzyme. Using basolateral membrane vesicles, an increased ATP-dependent ouabain-sensitive sodium transport was also demonstrated in MHS rats. These results support the hypothesis that a higher tubular sodium reabsorption may be involved in the pathogenesis of hypertension in this rat strain.

Animals↗
PubMed1979

[On the effect of cadmium on tissue respiration and gluconeogenesis in rat kidney cortex (author's transl)].

Oxygen consumption (QO2), respiratory quotient (RQ) and gluconeogenesis of rat kidney cortex slices were determined (Warburg technique). QO2 was not influenced by 0.01 mM CdCl2 in the incubation medium (no exogenous substrate added), 0.1 mM, 1mM and 10 mM, respectively, reduced QO2 by 43%, 45% and 68%. In the presence of 8 mM glucose, 10 mM acetate or 5 mM butyrate, 1 mM Cd resulted in a decrease in QO2 by about 50% each. Addition of 20 g/l albumine to the medium abolished this effect of cadmium. RQ was not influenced by a mM Cd, both without and with 8 mM glucose in the medium. Glucose production from 7 mM pyruvate or 5 mM glutaminate in slices from fed and starving rats was reduced by 1 mM Cd to half the value found in controls.

Albumins↗
PubMed1972

Transport and metabolism of galactose in rat kidney cortex.

1. Analysis of transport of d-galactose was complicated by metabolism of the compound but appeared to have two components: a substrate-saturable component and a diffusion component. At low substrate concentration (<1mm) active transport was observed. Accumulation of galactose was largely independent of Na(+) concentration. The apparent K(m) for this component was 0.2mm. At substrate concentrations above 1mm the active transport system appeared saturated and further increases in substrate concentration resulted in a linear increase in the rate of galactose accumulation, but no concentration gradient was formed. 2. d-[1-(14)C]Galactose (2mm) was metabolized to (14)CO(2) by rat kidney-cortex slices incubated at 37 degrees C, at the rate of 68nmol/h per 100mg of tissue. 3. Intracellular components from such incubations were separated into a neutral fraction, the only major labelled component being galactose, and a phosphorylated fraction. 4. Phosphorylated metabolites found in galactose-incubated slices increased with increasing substrate concentration and achieved a limiting value of 0.42mm after 60min of incubation. 5. Galactose uptake was inhibited by anaerobiosis, dinitrophenol and phlorrhizin. 6. Methyl alpha-d-glucoside and d-glucose partially inhibited galactose uptake only at ratios of 100:1. 7. The presence of pyruvate did not decrease galactose metabolism although it did decrease production of (14)CO(2) from [1-(14)C]galactose. Gluconeogenesis occurred in the presence of pyruvate and (14)C from galactose was found in glucose. 8. Rat kidney-cortex slices metabolized 2mm-[1-(14)C]galactonate to (14)CO(2) at a rate of 20nmol/h per 100mg of tissue.

Anaerobiosis↗
PubMed1977

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.

Acidosis↗
PubMed1981

Phosphoenolpyruvate efflux from kidney cortex mitochondria of rabbit.

(1) The relationship between phosphoenolpyruvate formation and its accumulation in kidney cortex mitochondria of rabbit was studied in the presence of glutamate as substrate. (2) In mitochondria incubated in either State 4 or under uncoupled conditions, both 1,2,3-benzenetricarboxylate and atractyloside resulted in a marked elevation of the intramitochondrial phosphoenolpyruvate accompanied by a 2-4-fold decline in production of this compound. The same effect was induced by n-butylmalonate in uncoupled mitochondria, while both phosphoenolpyruvate efflux and its production were inhibited to a smaller extent in mitochondria incubated with 1,2,3-benzenetricarboxylate in State 3. (3) Citrate, malate or 2-phosphoglycerate caused a fast displacement of phosphoenolpyruvate from atractyloside-inhibited mitochondria to the reaction medium. In contrast, on the addition of ATP to mitochondria incubated with 1,2,3-benzenetricarboxylate, the rate of phosphoenolpyruvate efflux was lower than that induced by either malate or citrate. (4) Despite the presence of both 1,2,3-benzenetricarboxylate and atractyloside, arsenite and rotenone plus antimycin resulted in a leakage of phosphoenolpyruvate from the mitochondria, probably via a carrier-independent mechanism. (5) Based on the present results it seems that depending on the metabolic condition, the tricarboxylate carrier and the adenine nucleotide translocase are functioning to different extents in the efflux of phosphoenolpyruvate from rabbit renal mitochondria to the surrounding medium.

Animals↗
PubMed1984

Cooperation of Ca2+ and pH in regulation of the activity of the 2-oxoglutarate dehydrogenase complex and its components from bovine kidney cortex.

A modified procedure for preparation of the 2-oxoglutarate dehydrogenase complex from bovine kidney cortex is presented. The enzymatic preparation obtained showed a specific activity of 18.5 mumol X min-1 X mg-1. This activity was dependent on Ca2+ (1-40 microM) and hydrogen ion concentration. At pH 7.6 in the absence of Ca2+ (less than 10(-9) M), S0.5 for 2-oxoglutarate was 2.5 mM, and in the presence of Ca2+ it was decreased to 0.3 mM. The maximum reaction rate at this pH was increased by Ca2+ by 33%. The increase of pH from 7.0 to 8.4 resulted in a 150-fold increase of S0.5. The activity of 2-oxoglutarate decarboxylase, a subunit of the dehydrogenase complex, was also dependent on Ca2+ and pH. The activity of 2-oxoglutarate decarboxylase, determined in the presence of ferrocyanide as electron acceptor, showed three different partial Michaelis constants for 2-oxoglutarate, low (K1m), medium (K2m) and high (K3m). At pH 6.9, K3m was 0.11 mM, and 0.005 mM in the absence and presence of Ca2+, respectively. The maximum reaction rate at pH 6.9 in the presence of Ca2+ was by 72% higher than in its absence. A change of pH from 6.9 to 7.6 led to an increase in K1m from 0.005 to 0.01 mM, and K3m from 0.11 to 0.60 mM. Ca2+ had no effect on the activity of lipoamide dehydrogenase or lipoamide succinyltransferase. These results indicate that, over the pH range 6.5 - 7.2, calcium ions affect the activity of the whole complex by regulating the activity of 2-oxoglutarate decarboxylase, whereas over the pH range 7.2 - 8.4 they affect the activity of the 2-oxoglutarate dehydrogenase complex by acting on the structure of the whole complex rather than by changing the activity of 2-oxoglutarate decarboxylase.

Animals↗
PubMed1975

On the mechanism of malonyl-CoA-independent fatty-acid synthesis. Characterization of the mitochondrial chain-elongating system of rat liver and pig-kidney cortex.

1. Chain elongation of fatty acids by extracts of mitochondrial acetone powders from rat liver and pig kidney cortex are similar in their properties. The specific activity of the kidney system is about 30% as compared to the liver system 2. Different incorporation rates [1-14-C] acetate into fatty acids in the presence of NADH as the sole hydrogen donor that were reported in literature can be explained by different extraction methods. 3. In liver the incorporation into the saturated fatty acid, elongated by one C-2 unit, amounts to only 19% with NADH and 60% with NADPH in comparison with the incorporation in presence of both nucleotides. 4. Kinetics of the chain-elongating process favour the enoyl-CoA reductase to be the rate limiting step. 5. Long-chain saturated and unsaturated fatty acyl-CoA derivatives are very poor primers of the chain elongation. 6. Possion and the enoyl-CoA reductase may be the transfer of hydrogen from NADPH to the respiratory chain, and the conservation of reducing equivalents (NADH and NADPH) or acetate units during cellular anoxia.

Acetates↗
PubMed1993

Cloning of a rabbit kidney cortex AT1 angiotensin II receptor that is present in proximal tubule epithelium.

The rabbit proximal tubule (PT) has been widely utilized to study the direct effects of angiotensin II (ANG II) on PT function. The purpose of the present study was to characterize the binding properties of PT ANG II receptors, using nonpeptide antagonists, and to clone a rabbit PT ANG II receptor. In rat and rabbit kidney cortical brush-border and basolateral membranes, specific binding of 125I-ANG II was inhibited by the AT1 ANG II-receptor antagonist DuP 753, but not by the AT2 antagonist PD 123319. Using a rabbit kidney cortex cDNA library, we isolated cDNA encoding an ANG II receptor, with an open-reading frame sharing a high degree of sequence homology to previously cloned AT1 ANG II receptors. In transfected COS-1 cells, this rabbit ANG II receptor had properties of the AT1 class. Northern analysis revealed high levels of mRNA expression for this receptor in rabbit kidney cortex and adrenal gland. Within the kidney, message was detected in primary cultures of rabbit PT cells, as well as in freshly isolated rabbit PT segments. Message was also present in cells of the mouse PT line, MCT, and in rat glomerular mesangial cells. Utilizing polymerase chain reaction (PCR) with primers derived from the 1st and 4th transmembrane domains of the rat AT1A ANG II receptor, a 279-bp DNA fragment was amplified from reverse-transcribed RNA from rabbit PT cells. This DNA encoded an amino acid sequence identical to that encoded by the rabbit kidney cDNA clone in the corresponding region and differed by a single base substitution. Southern analysis of rabbit genomic DNA restriction digests with the rabbit ANG II receptor probe revealed hybridization to a single band in each lane. These results indicate that an AT1 ANG II receptor is present in the PT and that a single gene codes for the AT1 receptor in rabbit. The clone isolated in the present study should provide a useful tool with which to study the regulation of the PT renin-angiotensin system.

Amino Acid Sequence↗
PubMed1992

[The age-related characteristics of the hormonal regulation of Na+, K(+)-ATPase activity in the kidney cortex of rats].

The aldosterone binding in isolated distal convoluted and cortical collecting tubules of renal nephrons and the influence of hormonal induction on the Na, K-ATPase activity in membrane fraction of kidney cortex were studied in 10-day- and 2-month-old rats. No reliable difference in aldosterone-specific binding was revealed (0.26 +/- 0.04 and 0.22 +/- 0.03 fmol/mm of tubule length, respectively, at the age of 10 days and 2 months). It was found that Na, K-ATPase activity increased with age from 0.39 +/- 0.06 to 0.72 +/- 0.10 mumol Pi/mg of protein.1 hour.100 microliters. Aldosterone induction caused approximately a 3-fold increase of the enzyme activity in both age groups comparing to the control level. Co-induction of aldosterone and spironolactone resulted in a 50% decrease of Na, K-ATPase activity in adult rats, but did not influence that in young rats. The revealed age-related differences in the mechanism of hormonal Na, K-ATPase regulation are supposed to underlie the absence of physiological reaction of the kidney to aldosterone in early postnatal ontogenesis.

Adrenalectomy↗