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A Tejedor

Publications and source records attributed to A Tejedor.

34 records · Page 2Linked to original sources
PubMed1991

Dietary NaCl modulates Na(+)-H+ antiporter activity in renal cortical apical membrane vesicles.

An apical membrane Na(+)-H+ antiporter mediates proximal tubule NaCl and NaHCO3 reabsorption. The present studies examined whether chronic changes in dietary NaCl intake lead to an adaptation of the Na(+)-H+ antiporter. Rats were maintained either on a low-salt (LS, 0% NaCl) or a high-salt (HS, 2% NaCl) diet for 4 days. Na(+)-H+ antiporter was assayed using the acridine orange fluorescence method in apical membrane vesicles prepared by Mg2+ aggregation. Rats on LS diet exhibited a higher maximal activity (Vmax) for antiporter activity (0.109 +/- 0.008 s-1) compared with rats on HS diet (0.090 +/- 0.008 s-1; P less than 0.01), whereas Na activity (KNa) was similar (13.1 +/- 1.5 and 14.2 +/- 0.8 mM in HS and LS groups, respectively). The modulation of Na(+)-H+ antiporter activity was amiloride sensitive. Proton permeability, Na(+)-dependent [3H]glucose uptake, and vesicle enrichments were similar in both groups. In addition, the dietary protocols were not associated with any systemic acid-base disturbances, K+ deficiency, or hyperfiltration, conditions that have previously been demonstrated to alter Na(+)-H+ antiporter activity. Acute differences in extracellular fluid volume, induced by 10% body weight isohydric expansion failed to affect Na(+)-H+ antiporter activity. Thus chronic alterations in dietary NaCl intake alter the maximal activity (Vmax) of the Na(+)-H+ antiporter. This adaptation may contribute to decreased NaCl reabsorption in extracellular fluid volume expansion, enhanced NaCl reabsorption in extracellular fluid volume depletion, and enhanced NaHCO3 reabsorption in chronic metabolic alkalosis associated with volume contraction.

Animals↗
PubMed1991

Metabolism of lactate by a suspension of dog thick ascending limbs: relations with transport.

The addition of substrate in the form of lactate (L), but not glucose (G), increases the respiration of canine thick ascending limb (TAL) segments in a saturable (above 2 mM) fashion. More than 60% of this stimulation is ouabain-sensitive (1 mM ouabain) even if L and G transport are both sodium-insensitive processes in TAL. Thus L, but not G, specifically stimulates Na+ entry in TAL cells and its subsequent transport by the Na+,K(+)-ATPase. If chloride is substituted for by gluconate, no significant substrate-induced stimulation of ouabain-sensitive respiration is observed. SITS (4-acetamino-4'-isothiocyanostilbene-2,2'-disulfonic acid) also interferes with the L-induced stimulation of respiration. Thus L entry in TAL appears to be directly or indirectly coupled to the transepithelial flux of Cl-. Furosemide (F), but not amiloride, also inhibits this stimulation suggesting that the accelerated Na+ entry triggered by the application of L occurs through the F-sensitive carrier or that lactate transport is F-sensitive in TAL cells. In accord, F specifically impairs the metabolism of L (as compared to G). These data suggest that in intact TAL tubules both lactate uptake and oxidation are directly or indirectly influenced by the transcellular flux of NaCl. This organization may participate to maintain a stoichiometry between the transport of NaCl and the availability of L to support the energetic needs of TAL cells.

Animals↗
PubMed1991

Chronic adaptations in proximal tubular H/HCO3 transporters.

Chronic acidosis, chronic K deficiency, and chronic hyperfiltration all lead to similar parallel increases in Na/H antiporter and Na/3HCO3 cotransporter activities. These effects persist when the transporters are removed from the inducing environment, and thus represent memory effects. The effect of acidosis on the Na/H antiporter can be reproduced by preincubating cultured proximal tubule cells chronically in acid media, suggesting that low extracellular fluid pH is an important signal in acidosis. The specific extracellular signals in chronic K deficiency and chronic hyperfiltration have not been elucidated. The effect of acid preincubation on Na/H antiporter activity in cultured proximal tubule cells is dependent on protein synthesis and is associated with increased abundance of mRNA for the Na/H antiporter. The cell signalling pathways which mediate these effects have not been determined. However, the common response in chronic acidosis, chronic K deficiency, and chronic hyperfiltration to the demand for increased H transport, suggests that a common signalling pathway will be found in all these conditions.

Adaptation, Physiological↗
PubMed1990

Preincubation in acid medium increases Na/H antiporter activity in cultured renal proximal tubule cells.

Chronic acidosis in vivo leads to an increase in proximal tubule Na/H antiporter activity that persists when the transporter is studied out of the acidotic environment. It is presently not clear whether a decrease in extracellular fluid pH alone is sufficient to elicit this adaptation. The present studies examined the effect of acid preincubation on Na/H antiporter activity in cultured proximal tubule cells. Antiporter activity was examined after a 2-day preincubation in control or acid medium, 1 hr after removal from the preincubation fluid. Na/H antiporter activity was assayed as the initial rate of Na-dependent alkalinization after cell acidification in the absence of CO2/HCO3. Preincubation in low [HCO3] acid medium or in high PCO2 acid medium led to increases in amiloride-sensitive Na/H antiporter activity. This adaptation was inhibited by addition of cycloheximide to the preincubation medium. Preincubation of fibroblasts in low [HCO3] acid medium did not lead to increased Na/H antiporter activity but rather caused a small inhibition. These studies demonstrate an adaptation in Na/H antiporter activity elicited by a low pH of the extracellular fluid, which is dependent on protein synthesis, and may be unique to certain H/HCO3-transporting epithelia.

Amiloride↗
PubMed1990

Basolateral transport of lactate in dog thick ascending limbs.

Basolateral membrane vesicles (BLMV) isolated from both red outer medulla or from thick ascending limb segments isolated from the dog kidney were used to examine the process of lactate transport in this nephron segment. The BLMV preparation was enriched in Na(+)-K(+)-adenosinetriphosphatase (Na(+)-K(+)-ATPase) that represented 96% of the total ATPase activity of this preparation and the vesicles were largely under the right side-out orientation. On application of a OH- or HCO3- gradient (inside greater than outside), a secondary active lactate accumulation was observed, with characteristic transient overshoot. This phenomenon was shown to occur irrespective of the presence or absence of Na+, K+, or Cl-. The pH, but not the bicarbonate-driven, overshoot was abolished by nigericin (in presence of K+). Studies with valinomycin and K+ demonstrated that the generation of a membrane potential was not responsible for the acceleration of lactate transport, even if the amplitude of lactate accumulation was reduced in the presence of a bicarbonate gradient and valinomycin. A significant trans-stimulation of [14C]lactate transport by cold lactate was observed (under voltage-clamp condition). The transport was 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid insensitive but sensitive to furosemide (IC50 = 0.1 mM) and alpha-hydroxycyanocinnamate (IC50 = 1 mM). The kinetic parameters of the transporter revealed a single carrier with an apparent Michaelis constant of 1.7 mM and an apparent Vmax of 9.7 nmol.mg protein-1.30 s-1. The transporter was shown to be distinct from that of proximal tubule brush-border membrane or mitochondria (pyruvate). Thus thick ascending limbs possess a carrier-mediated lactate transport that can be used for lactate uptake (aerobic condition) or for lactate release (anaerobic glycolysis) according to metabolic processes imposed by the local oxygenation condition.

Animals↗
PubMed1988

Absence of an endogenous regulator of Na+,K+-ATPase activity in the tissues of cirrhotic rats.

Microsomal Na+,K+-ATPase isolated from the renal cortex of rats with CCL4-induced cirrhosis (CIR) showed a higher specific activity than the enzyme obtained from control rats (COR). Kinetic studies showed a lower K0.5 for ATP (0.08 +/- 0.03 vs. 0.24 +/- 0.04 mM; p less than 0.05), a lower Na+ activation constant (9.6 +/- 1.5 vs. 19.0 +/- 1.7 mM; p less than 0.05), and a higher K+ activation constant (1.2 +/- 0.1 vs. 0.6 +/- 0.1 mM; p less than 0.05) for CIR. The optimal pH of the enzyme was 0.5 units higher in CIR than COR. The fluorescence of eosin-treated enzymes indicated a higher ratio of E1/E2 forms of Na+,K+-ATPase in CIR. The K+-activated p-nitrophenylphosphatase (pNPPase) activity of the enzyme was lower in CIR than COR rats (1.5 +/- 0.1 vs. 2.2 +/- 0.1 mU/mg; p less than 0.05). Dialysing (24 h) COR microsomes reproduced most of the changes observed in CIR enzymes (kinetics, optimal pH, and eosin fluorescence). Lyophilized dialysate of COR, but not of CIR microsomes, inhibits Na+,K+-ATPase activity. These results suggest that a dialysable inhibitor modifies the Na+,K+-ATPase activity in the kidney of COR which is almost absent in that of CIR. The absence of this factor may lead to the overall inability to excrete Na+ in the cirrhotic state.

Animals↗
PubMed1988

Characterization and metabolism of canine proximal tubules, thick ascending limbs, and collecting ducts in suspension.

Preparations of distinct nephron segments were obtained from dog kidneys by collagenase treatment. Four morphologically different tissues were isolated: glomeruli, proximal tubules, thick ascending limbs, and papillary collecting ducts. Each segment possessed a characteristic assay of membrane-bound and cytoplasmic enzymes. Specific metabolic characteristics also were found: gluconeogenesis and ammoniagenesis in proximal tubules, glycolytic aerobic metabolism in thick ascending limbs, and glycolytic anaerobic metabolism in papillary collecting ducts. The assay of Na+ -K+ ATPase, H+ -ATPase, and Ca2+ -ATPase activities in these nephron segments demonstrated a specific enrichment of Na+ -K+ ATPase in thick ascending limbs, and of H+ -ATPase in proximal tubules and papillary collecting ducts. Tubular respiration in the absence or presence of ouabain, 1,3-dicyclohexylcarbodiimide, or furosemide demonstrated that the respiration of each segment could be correlated to the activity of specific ion motive ATPases. Furthermore, a tight coupling between ion transport, ATP turnover, and substrate oxidation was demonstrated. These isolated tubular structures are thus viable and capable of transepithelial transport. Our preparation provides large amounts of defined population of tubules and are thus useful for the study of biochemical and functional heterogeneity along the nephron.

Adenosine Monophosphate↗
PubMed1988

Biochemical characterization and osmolytes in papillary collecting ducts from pig and dog kidneys.

Papillary collecting duct tubules were prepared in gram quantities from the papillae of dog and pig kidneys. Measurements of substrate and oxygen utilizations by these tubules under both aerobic and anaerobic conditions showed the potential for both glycolysis and oxidative phosphorylation. Oxygen is not necessary to maintain a normal adenosine 5'-triphosphate concentration, but oxidative phosphorylation contributes to more than 65% of the metabolism under aerobic conditions in the two species. Both phosphorus-31 and proton nuclear magnetic resonance spectra recorded from extracts of dog cortex, red medulla, and papilla showed a clear gradient from cortex to papilla for osmolytes, such as glycerophosphorylcholine, sorbitol, inositol, betaine, and sugar phosphates. Other molecules identified in the spectra included glucose, sorbitol, mannitol, lactate, glutamine, alanine, threonine, and adenosine 5'-triphosphate. Conventional biochemical measurements supported these findings. An increase in osmolality from 300 to 600 mosmol/kg H2O for 120 min did not increase the glycerophosphorylcholine and sorbitol concentrations of dog papillary collecting ducts in vitro, but a small effect of a 24-h dehydration was detected in vivo.

Adenine Nucleotides↗
PubMed1987

Effect of acetazolamide on renal metabolism and ammoniagenesis in the dog.

The effect of acetazolamide (ACZ) on renal metabolism and ammoniagenesis was studied in the dog in vivo and in vitro. ACZ was administered to 10 dogs with normal acid-base status and five with chronic metabolic acidosis induced by NH4Cl. In both groups of dogs, the acute administration of ACZ markedly reduced the urinary excretion of ammonium (from 33 to 10 in normal dogs and from 100 to 23 mumoles/100 ml GFR in acidotic dogs) whereas its release into the renal vein was increased in a reciprocal fashion (from 69 to 95 in normal dogs and from 91 to 152 mumoles/100 ml GFR in acidotic dogs). ACZ did not change the total ammonium production nor the renal glutamine utilization. The renal utilization or production of glutamate, alphaketoglutarate, alanine and citrate also remained unchanged. Despite a marked urinary alkalinization, citraturia remained minimal. However, the renal cortical concentrations of glutamine, glutamate, succinate, fumarate, malate, aspartate and phosphoenolpyruvate fell following ACZ administration, especially in acidotic dogs showing rapid renal utilization of glutamine. ACZ had no effect on the same metabolites in the kidney of normal dogs even when lactate utilization was enhanced by lactate infusion. This study demonstrates that an accelerated ammoniagenic flux can proceed in the dog kidney without the renal cortical changes produced by metabolic acidosis in this species. In vitro, using dog tubules, a selective effect of ACZ on glutamine metabolism as compared to lactate was observed. ACZ reduce the rate of the reactions catalyzed by alphaketoglutarate dehydrogenase and by succinyl CoA synthetase. Other enzymes of the ammoniagenic and gluconeogenic pathways (glutaminase, GLDH, malic enzyme, PEPCK) were not changed by ACZ. The metabolic effects of ACZ observed in the intact kidney in vivo or with tubules in vitro may be in part related to the effect of ACZ on these enzymes critical for the ammoniagenic process.

Acetazolamide↗
PubMed1987

Acetate metabolism during hemodialysis: metabolic considerations.

Acetate is used during regular hemodialysis to replace the bicarbonate lost during dialysis. The temporal changes of plasma bicarbonate and acetate concentrations and the critical role of acetate metabolism for the maintenance of plasma bicarbonate are described. We point out that the maximal rate of acetate oxidation in man is usually reached during dialysis, and we identify physiologic and pathologic factors that may modify this Vmax. A syndrome of 'intolerance to acetate' has been described. This syndrome is analyzed in the light of the metabolic consequences of a rapid flux of acetate oxidation in liver and muscle cells. More specifically, the effects of rapid acetate metabolism on tissue ATP, CoA, adenosine and other ATP degradation products are presented. The possible impact of dialysis-induced depletion of carnitine on optimal acetate metabolism is discussed. The potential clinical consequences produced by these changes are presented in relation to the symptoms sometimes observed during dialysis against acetate: vasodilation, hypotension and angina pectoris. The hypoxemia induced by acetate is also briefly reviewed. Different directions are proposed for future research.

Acetates↗
PubMed1985

Lack of effect of synthetic atrial natriuretic factor on rubidium uptake by human erythrocytes.

The effect of synthetic atrial natriuretic factor on the ouabain-sensitive and the furosemide-sensitive rubidium uptake by human erythrocytes has been studied. This peptide with potent diuretic and natriuretic effects did not affect any rubidium uptake system at concentrations of 10(-7) and 10(-9) M. These results do not support that the natriuretic effect is based on the inhibition of active transport systems in the renal tubules.

Atrial Natriuretic Factor↗
PubMedDate not supplied

Fluorescence measurement of intracellular pH on proximal tubule suspensions. The need for a BCECF sink.

BCECF is used for intracellular pH (pHi) measurement in microperfused tubules. In this case, the perfusate washes out all BCECF leaking from the cells away from the optical light path. We have explored the use of BCECF for pHi determination on suspensions of dog renal proximal tubules (Percoll). This raises specific problems due to the accumulation of BCECF in the extracellular compartment generated by desesterification of BCECF-AM during loading and to leaking of BCECF into the extracellular medium occurring during the waiting time and during the measurement procedure. Repeated washing of the suspension reduced in part this contamination but did not eliminate the continuous leakage of BCECF: the specific intracellular signal is progressively reduced. We have examined the use of anion exchange resin (Dowex 1X-8, 200-400 mesh, Cl- form) to bind the extracellular BCECF (negatively charged). Dowex beads glued to one wall of the cuvette out of the optical path constitute an optically neutral sink removing BCECF as it leaks out of the cells. Using this technique, we had estimated the pHi of dog proximal tubule to 7.374 +/- 0.032 at extracellular pH of 7.325 +/- 0.021. The cellular pH is acutely, but transiently, alkalinized by NH4Cl and acidified by Na acetate. The BCECF signal was calibrated using nigericin. This technique improves significantly the measurement of pHi by BCECF fluorescence in tissue suspensions.

Animals↗
PubMedDate not supplied

Glucose metabolism in dog inner medullary collecting ducts.

The adenosine triphosphate (ATP) generating pathways of dog inner medullary collecting ducts (IMCD) were examined in vitro using suspensions of dog IMCD tubules incubated under aerobic and anaerobic conditions. Glucose is always the preferred substrate for this tissue, even if lactate can be oxidized under aerobic conditions. The metabolism of glucose proceeds largely towards lactate accumulation in the presence or absence of oxygen. Glycogen is also consumed and more markedly so during anoxia. The pentose shunt represents a minor pathway for glucose metabolism in this tissue. Under aerobic conditions, the net oxidation of glucose to CO2 contributes significantly to the cell energetics, mitochondrial and cytoplasmic mechanisms sharing equally the ATP synthesis. In the absence of oxygen, only the cytoplasmic routes of ATP synthesis are used, but the apparent ATP turnover is markedly reduced. A marked inhibition of the activity of the Na-K-ATPase during anoxia explains this observation. The utilization of glucose for osmolyte synthesis is a minor process and appears to be suppressed under anaerobic conditions. It is concluded that the ATP turnover is low in dog IMCD cells as compared with that of other nephron segments and is largely dependent upon glucose availability under aerobic or anaerobic conditions.

Adenosine Triphosphate↗
PubMedDate not supplied

Determination of imidacloprid and benzimidazole residues in fruits and vegetables by liquid chromatography-mass spectrometry after ethyl acetate multiresidue extraction.

A simple and sensitive method based on liquid chromatography-atmospheric pressure ionization-mass spectrometry is described for the determination of 4 benzimidazole pesticides (carbendazim, thiabendazole, benomyl, and thiophanate-methyl) and imidacloprid in vegetables and fruits. Food samples were typically extracted with ethyl acetate to draw the analytes into the organic phase. No cleanup step was necessary before injection into the liquid chromatographic (LC) system with electrospray mass spectrometric detection. The analytes were separated on a reversed-phase C8LC column. Limits of detection for the compounds were in the microg/L range. Results are reported for validation studies with fortified pear and tomato samples and for residues of the target compounds found in the pesticide residue monitoring program during 1998.

Acetates↗
PubMedDate not supplied

Cross-talk between the Na(+)-K(+)-ATPase and the H(+)-ATPase in proximal tubules in suspension.

The cellular energy required for the activity of the Na(+)-K(+)-ATPase and of the H(+)-ATPase was estimated in intact proximal tubules in suspension. Both the fall in oxygen consumption (directly measured) and NADH oxidation (as estimated from exogenous substrate metabolism) were measured before and following application of ouabain (1 mM) to inhibit the sodium pump, following bafilomycin (0.1 mM) to inhibit the proton pump or following a combination of these inhibitors. The data demonstrate that the sodium pump utilizes 43% and the proton pump 19% of the phosphorylating NADH turnover of canine proximal tubules studied in vitro. However, a significant and stoichiometric stimulation of one pump was observed upon inhibition of the other. The NADH turnover related to the sodium pump increased from 308 to 402 (delta = 94) mumol.g-1 wet weight.h-1 following bafilomycin application and that of the proton pump from 136 to 230 (delta = 94) following ouabain application. This stimulation was largely abolished by inhibition of the Na+/H+ exchange occurring in either direction by amiloride or methylisobutylamiloride. It is concluded that a cross-talk occurs between the basolateral sodium pumps and the proton pumps located on the brush border membrane and/or on endosomes in proximal tubules. This cross-talk appears to be mediated by Na+/H+ exchange suggesting that both the proton pump and the Na+/H+ exchanger may contribute in a cooperative fashion to the proximal secretion of protons.

Amiloride↗