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Biomedical subjects

M Moretó

Publications and source records attributed to M Moretó.

At least 19 recordsLinked to original sources
PubMed2005

Transepithelial taurine transport in caco-2 cell monolayers.

Here we characterized transepithelial taurine transport in monolayers of cultured human intestinal Caco-2 cells by analyzing kinetic apical and basolateral uptake and efflux parameters. Basolateral uptake was Na(+)- and Cl(-)- dependent and was inhibited by beta-amino acids. Uptake by this membrane showed properties similar to those of the apical TauT system. In both membranes, taurine uptake fitted a model consisting of a non-saturable plus a saturable component, with a higher half-saturation constant and transport capacity at the apical membrane (K(m), 17.1 micromol/L; V(max), 28.4 pmol.cm(-2).5 min(-1)) than in the basolateral domain (K(m), 9.46 micromol/L; V(max), 5.59 pmol.cm(-2).5 min(-1)). The non-saturable influx component, estimated in the absence of Na(+) and Cl(-), showed no significant differences between apical and basolateral membranes (K(D), 89.2 and 114.7 nL.cm(-2) . 5 min(-1), respectively). Taurine efflux from the cells is a diffusive process, as shown in experiments using preloaded cells and in trans-stimulation studies (apical K(D),72.7 and basolateral K(D), 50.1 nL.cm(-2).5 min(-1)). Basolateral efflux rates were significantly lower than passive influx rates. We conclude that basolateral taurine uptake in Caco-2 cells is mediated by a transport mechanism that shares some properties with the apical system TauT. Moreover, calculation of unidirectional and transepithelial taurine fluxes reveals that apical influx of this amino acid is higher than basolateral efflux rates, thereby enabling epithelial cells to accumulate taurine against a concentration gradient.

Biological Transport↗
PubMed2005

Aldosterone reduces crypt colon permeability during low-sodium adaptation.

Fluid and electrolyte absorption by colonic crypts depends on the transport properties of crypt cellular and paracellular routes and of the pericryptal sheath. As a low-Na(+) diet increases aldosterone and angiotensin II secretion, either hormone could affect absorption. Control and adrenalectomized (ADX) Sprague-Dawley rats were kept at a high-NaCl (HS) diet and then switched to low-NaCl (LS) diet for 3 days. Aldosterone or angiotensin II plasma concentrations were maintained using implanted osmotic mini-pumps. The extracellular Na(+) concentration in isolated rat distal colonic mucosa was determined by confocal microscopy using a low-affinity Na(+) -sensitive fluorescent dye (Sodium red, and Na(+) -insensitive BODIPY) bound to polystyrene beads. Crypt permeability to FITC-labelled dextran (10 kDa) was monitored by its rate of escape from the crypt lumen into the pericryptal space. Mucosal ion permeability was estimated by transepithelial electrical resistance (TER) and amiloride-sensitive short-circuit current (SCC). The epithelial Na(+) channel, ENaC, was determined by immunolocalization. LS diet decreased crypt wall permeability to dextran by 10-fold and doubled TER. Following ADX, aldosterone decreased crypt wall dextran permeability, increased TER, increased Na(+) accumulation in the pericryptal sheath and ENaC expression even in HS. Infusion of angiotensin II to ADX rats did not reverse the effects of aldosterone deprivation. These findings indicate that aldosterone alone is responsible for both the increase in Na(+) absorption and the decreased paracellular and pericryptal sheath permeability.

Adaptation, Physiological↗
PubMed2005

Pericryptal myofibroblast growth in rat descending colon induced by low-sodium diets is mediated by aldosterone and not by angiotensin II.

Pericryptal myofibroblast growth in descending colonic crypts correlates with the activation of the renin-angiotensin-aldosterone system. Earlier work showed that during the transition from a high-Na(+) (HS) to low-Na(+) (LS) diet there are changes in the colonic crypt wall and pericryptal sheath. As LS diet increases both aldosterone and angiotensin II, the aim here was to determine their individual contributions to the trophic changes in colonic crypts. Experiments were conducted on control and adrenalectomized Sprague-Dawley rats fed an HS diet and then switched to LS diet for 3 days and supplemented with aldosterone or angiotensin II. The actions of the angiotensin-converting enzyme inhibitor captopril, the angiotensin receptor antagonist losartan and the aldosterone antagonist spironolactone on extracellular matrix proteins, claudin 4 and E-cadherin myofibroblast proteins, alpha-smooth muscle actin (alpha-SMA) and OB-cadherin (cadherin 11), angiotensin type 1 and TGFbetar1 membrane receptors were determined by immunolocalization in fixed distal colonic mucosa. The LS diet or aldosterone supplementation following ADX in HS or LS increased extracellular matrix, membrane receptors and myofibroblast proteins, but angiotensin alone had no trophic effect on alpha-SMA. These results show that aldosterone stimulates myofibroblast growth in the distal colon independently of dietary Na(+) intake and of angiotensin levels. This stimulus could be a genomic response or secondary to stretch of the pericryptal sheath myofibroblasts accompanying enhanced rates of crypt fluid absorption.

Adaptation, Physiological↗
PubMed2005

Diagnosis of esophagogastric tumors.

With regard to esophageal tumors, important reports on several topics have been published recently. 1) The place of endoscopic ultrasonography (EUS) as the best locoregional staging technique for cancer of the esophagus has been further consolidated. The addition of fine-needle aspiration makes EUS more sensitive than computed tomography (CT) and more accurate than CT or EUS alone for nodal staging. 2) High-resolution endoscopy with chromoendoscopy has been found to be very effective for mucosal lesions, but not for submucosal lesions. In combination with EUS, the sensitivity for submucosal tumors increases up to 60 %. 3) Autofluorescence-guided biopsy has been reported to be a good tool for detecting high-grade dysplasia. A narrow-band imaging system improved the overall accuracy for depth of invasion. 4) The incidence of hypopharyngeal cancer increases after resection for esophageal carcinoma. Patients with a scattered staining pattern after application of Lugol's solution are more prone to develop upper lesions. 5) Fluorescence imaging makes it possible to detect low-grade intraepithelial neoplasia in Barrett's mucosa, with fewer biopsies. 6) Patients with Barrett's esophagus with a length of over 3 cm had a significantly greater prevalence of dysplasia in comparison with those in the whom the Barrett's segment was shorter than 3 cm (23 % vs. 9 %, P = 0.0001). With regard to gastric tumors, 1) Helicobacter pylori eradication can significantly reduce the development of gastric cancer, but only in patients without precancerous lesions. 2) Intestinal metaplasia types II and III have been shown to have a higher rate of progression to low-grade dysplasia than type I. 3) With regard to screening in asymptomatic individuals, serum pepsinogen may represent an alternative to conventional fluoroscopy methods. 4) In patients who have undergone esophagectomy for esophageal cancer, annual follow-up endoscopies are vital for detecting early secondary gastric cancer and ulcerations in which curative treatment is possible. 5) High-resolution endoscopy allows more precise diagnosis of early gastric cancer. The presence of irregular minute vessels and variations in vessel caliber were found to be specific of early gastric cancer. The small regular pattern of sulci and ridges was observed significantly more frequently in differentiated carcinoma than in undifferentiated carcinoma. 6) Infrared-ray electronic endoscopy combined with indocyanine green injection appears to be effective in detecting sentinel nodes that contain metastases in patients with gastric cancer. 7) Gastric adenocarcinoma was found to show specific changes in the fluorescence spectra emitted, in comparison with normal gastric mucosa. However, there was wide variation in the emitted autofluorescence spectra in gastric cancer with signet-ring cells in comparison with normal mucosa.

Endoscopy, Digestive System↗
PubMed2003

Diagnosis of esophagogastric tumors.

It has been suggested that certain histological criteria may serve to indicate a good prognosis in patients with esophageal carcinoma. These include absence of subepithelial extension of the carcinoma cells, stage no higher than m2, and no neoplastic involvement near the resection margin. As endoscopic mucosal resection is becoming an accepted treatment option in this type of tumor, prognostic parameters of this type are of particular interest. By contrast, when metastases are detected in the celiac lymph nodes, it implies that the tumor is unresectable and that palliative treatment is required. Endoscopic ultrasound (EUS)-guided fine-needle aspiration has been found to be the most cost-effective option in this setting. Although autofluorescence endoscopy is being tested as a new technique for endoscopic diagnosis, its value is at present unclear. However, such developments may lead to improved diagnosis in the future, particularly in relation to the initial stages of carcinoma. For the moment, EUS is still the most widely accepted method for early diagnosis and staging. Esophageal squamous-cell carcinoma appears to be commonly associated with head and neck cancer, but the cost-effectiveness of surveillance is a matter of controversy. With regard to Barrett's esophagus and adenocarcinoma, p53 staining in areas of low-grade dysplasia appears to be helpful for predicting progression to high-grade dysplasia. The prevalence of short-segment Barrett's esophagus increases with age, but the length of the segment does not increase with time; the length probably depends on individual conditions, not merely on elapsed time. Helicobacter pylori infection appears to be associated with intestinal metaplasia at the esophagogastric junction. However, the most recent data appear to suggest that this scenario (usually termed "carditis") may be different from intestinal metaplasia in the lower esophagus, related to acid reflux. A follow-up program might be able to detect Barrett's esophagus adenocarcinoma at earlier stages, but only a minority of Barrett's esophagus patients are likely to be detected before neoplasia has developed. Gastric cancer appears to develop in individuals with H. pylori infection, but not in uninfected persons. In addition, those with severe gastric atrophy, corpus-predominant gastritis, and intestinal metaplasia may be at greater risk for gastric cancer. This again raises the question of H. pylori eradication in asymptomatic individuals with infection, and surveillance of patients with severe intestinal metaplasia. The most recent data appear to support the notion that healing of MALT lymphoma depends not only on H. pylori eradication and on the stage of the tumor, but also on individual factors (possibly immunology-related).

Adenocarcinoma↗
PubMed2001

Aldosterone mediates the changes in hexose transport induced by low sodium intake in chicken distal intestine.

1. In chickens, low Na+ diets markedly decrease the hexose transport in the rectal segment of the large intestine; transport in the ileum shows a lower, but significant reduction and transport in the jejunum is unaffected. These effects involve both apical (SGLT1) and basolateral (GLUT2) hexose transporters. 2. The role of the renin-angiotensin-aldosterone axis (RAAS) in the epithelial response to Na+ intake was studied in chickens fed high-NaCl (HS) and low-NaCl (LS) diets. The V(max) of alpha-methyl-D-glucoside and D-glucose were determined in vesicles from the brush-border (BBMVs) and basolateral (BLMVs) membranes, respectively. The binding of phlorizin to BBMV and cytochalasin B to BLMV were used as indicators of the abundance of SGLT1 and GLUT2, respectively. 3. In HS-adapted chickens, the serum concentration of aldosterone (means +/- S.E.M.) was 35 +/- 5 pg ml(-1) (n = 6) and that of renin was 20 +/- 2 ng ml(-1) (n = 3). In LS-fed birds, these values were 166 +/- 12 pg ml(-1) (n = 6) and 122 +/- 5 ng ml(-1) (n = 3), respectively. Administration of captopril, the inhibitor of the angiotensin-converting enzyme (ACE), to LS-chickens lowered the aldosterone serum concentration without affecting the renin concentration. Captopril also prevented the reduction of apical and basolateral hexose transport in ileum and rectum characteristic of the intestinal response to LS adaptation. 4. Administration of the aldosterone antagonist spironolactone to LS-adapted chickens did not affect the serum concentrations of aldosterone, but prevented the effects of LS intake on hexose transport in both apical and basolateral membranes. This suggests that the effects of aldosterone are mediated by cytosolic mineralcorticoid receptors. 5. Administration of exogenous aldosterone to HS-fed birds induced hexose transport and binding properties typical of the LS-adapted animals. These findings support the view that aldosterone, besides its primary role in controlling intestinal Na+ absorption, can also modulate the expression of apical and basolateral glucose transporters in the chicken distal intestine.

Aldosterone↗
PubMed2001

Sequential amino acid exchange across b(0,+)-like system in chicken brush border jejunum.

In the small intestine, cationic amino acids are transported by y(+)-like and b(0,+)-like systems present in the luminal side of the epithelium. Here, we report the characterization of a b(0,+)-like system in the apical membrane of the chicken jejunum, and its properties as an amino acid exchanger. Analysis of the brush border membrane by Western blot points out the presence of rBAT (protein related to b0,+ amino acid transport system) in these membranes. A functional mechanism for amino acid exchange across this system was established by kinetic analysis measuring fluxes at varying substrate concentrations both in internal (in) and external (out) vesicle compartments. This intestinal b(0,+)-like system functions for L-arginine as an obligatory exchanger since its transport capacity increases 100-200 fold in exchange conditions, thus suggesting an important role in the intestinal absorption of cationic amino acids. The kinetic analysis of Argin efflux velocities is compatible with the formation of a ternary complex and excludes a model involving a ping-pong mechanism. The binding affinity of Argout is higher than that of Argin, suggesting a possible order of binding (Argout first) for the formation of the ternary complex during the exchange cycle. A model of double translocation pathways with alternating access is discussed.

Amino Acid Transport Systems↗
PubMed2001

Diagnosis of esophagogastric tumors.

The incidence of esophageal tumors, and of adenocarcinoma in particular, has risen markedly in recent years in the developed countries. The use of a variety of histopathological and biological markers is now offering promising prospects for the future. Vertical tumor invasion, intratumoral microvessel density, antimucin monoclonal antibodies, flow cytometry, telomerase activity, and overexpression of cyclin D1 have been correlated with the staging and prognosis of esophageal carcinomas. By combining these markers with Lugol staining, a practical new method of staging esophageal tumors may become available in the coming years. As is well known, Barrett's mucosa is a preneoplastic condition. Discussions in the literature concerning short forms of Barrett's esophagus and their relationship to inflammation of the gastric cardia appear to describe two different scenarios--a gastroesophageal reflux condition for short forms of Barrett's esophagus, and an inflammatory phenomenon (perhaps unrelated to Helicobacter pylori infection) for inflammation of the gastric cardia. Cost-benefit studies of follow-up procedures in Barrett's esophagus have yet to be conducted, and considerable efforts--mainly using biological markers--are being made to identify those patients who are at greatest risk. Although the frequency of gastric tumors has declined in recent years, many as yet unclear aspects of these tumors have been studied. Technological progress has not led to substantial changes in the diagnostic procedures used, although autofluorescence methods and three-dimensional reconstruction have been analyzed. Laparoscopy, preferably combined with the use of ultrasound probes, may be a valuable tool for staging. The suggestion that endoscopy should be avoided in young patients (the "treat but do not scope" approach) has been seriously questioned, as it may lead to early cancer being overlooked. There is thought to be an intermediate stage of gastric cancer (between the early and advanced stages) in which the muscularis propria, but not the serosa, is invaded. Endoscopic ultrasonography is becoming increasingly established as a basic tool for the staging of gastric cancer. Gastric MALT lymphoma can be cured by H. pylori eradication therapy in many cases, but there is still uncertainty regarding the limitations of this approach.

Adenocarcinoma↗
PubMed2000

Effects of resalination on intestinal glucose transport in chickens adapted to low Na+ intakes.

In chickens, we have shown that intestinal absorption of glucose via apical SGLT1 and basolateral GLUT2 transport systems is affected by dietary Na+; low-Na+ adapted birds show a dramatic reduction of glucose transporters in both membranes in the rectum, an intermediate response in the ileum and no effects in the jejunum. We have now studied the effect of resalination of low-Na+ adapted chickens on glucose kinetics across SGLT1 (using -methyl-D-glucoside as substrate) and GLUT2 (using D-glucose) and on the specific binding of phlorizin and cytochalasin B, respectively. Twelve-week-old male Leghorn chickens were fed wheat and barley with drinking water containing either 150 mM NaCl (high-Na+ group) or 0. 015 mM (low-Na+ group) for 14 days (serum aldosterone: 242 +/- 6 pg ml-1 in the low-Na+ and 46 +/- 4 pg ml-1 in the high-Na+ group). On day 14, the low-Na+ group was either resalinated with an oral dose of NaCl (9 g (kg body wt)-1) or switched to the high-Na+ condition, for 1 week. Serum aldosterone measured 4 h, 1 day and 7 days after the change in NaCl intake fell to between 30 and 39 pg ml-1. The changes in apical -methyl-D-glucoside and basolateral D-glucose transport observed in the ileum and rectum of low-Na+ adapted animals were completely reversed by resalination within 4 h of NaCl administration to the level of values observed for high-Na+ adapted birds. The good correlation between the -methyl-D-glucoside and D-glucose Vmax and the SGLT1 and GLUT2 density, respectively, supports the view that the increase in apical and basolateral hexose transport found in the ileum and rectum of both groups of resalinated birds is due to an increase in the number of protein transporters. The rapid changes in the number of glucose transporters observed suggest that the target of the regulatory signal(s) involved are the mature enterocytes present in the villi rather than the developing enterocytes in the crypt.

Animals↗
PubMed1999

Hexose transport in the apical and basolateral membranes of enterocytes in chickens adapted to high and low NaCl intakes.

1. The effect of a low-NaCl diet (LS diet) on the properties of hexose transport across the brush-border and basolateral membranes of enterocytes from jejunum, ileum and rectum of the chicken was investigated. 2. In the brush-border membrane, LS adaptation had no effect on Km for alpha-methyl-D-glucoside while Vmax values were significantly reduced in the ileum and in the rectum. All Scatchard plots of specific [3H]phlorizin binding give a straight line, consistent with a single population of binding sites. Phlorizin binding vs. alpha-methyl-D-glucoside maximal transport rates showed a linear correlation. 3. In the basolateral membrane, the LS diet did not modify the Km for D-glucose but reduced the Vmax in the ileum and in the rectum. Scatchard plots of [3H]cytochalasin B binding support the view that there is a single transport system in this membrane. There was a linear correlation between cytochalasin B binding and D-glucose Vmax values. 4. The response of the chicken intestine to LS intake consists of a dramatic reduction in the number of glucose transporters in both apical and basolateral membranes of the rectum, an intermediate response in the ileum and no significant effects in the jejunum.

3-O-Methylglucose↗
PubMed1999

Electrical properties of the intestinal mucosa of the chicken and the effects of luminal glucose.

Transmural potential difference (PD), short-circuit current (Isc), and electrical resistance (R) were measured in the isolated mucosa of the duodenum, jejunum, ileum, proximal cecum, and rectum in order to characterize the electrical properties of the chicken small and large intestine. The chicken intestine was classified into three categories, regarding its electrical characteristics: 1) the duodenum, with four to five times higher R than the other segments and the lowest PD; 2) the group formed by the jejunum, the ileum, and the proximal cecum, with high PD and low R; 3) the rectum, with low PD and low R. In all segments, the addition of D-glucose into the luminal side stimulates Isc, and this effect can be reversed by phloridzin, indicating that the glucose-induced Isc increase is due to Na+-D-glucose co-transport. The effect of glucose is maximal in the rectum, with a fivefold Isc increase, suggesting that this segment may have an important role in the absorption of Na+ as well as of nutrients co-transported with Na+.

Animals↗
PubMed1999

Expression of Na+-D-glucose cotransporter in brush-border membrane of the chicken intestine.

We have studied the expression of Na+-D-glucose cotransporter in brush-border membrane vesicles (BBMVs) of chicken enterocytes to correlate the changes in the apical Na+-dependent transport with the changes in the amounts of transporter determined by Western blot analysis. Two different rabbit polyclonal antibodies were used simultaneously. The antibody raised against amino acids 564-575 of the deduced amino acid sequence of rabbit intestinal SGLT-1 (antibody 1) specifically detects a single 75-kDa band in the three segments, and this band disappeared when the antibody was preabsorbed with the antigenic peptide. The antibody raised against the synthetic peptide corresponding to amino acids 402-420 of the same protein (antibody 2) only reacts with jejunal and ileal samples, but no signal is found in BBMVs of rectum. Only when antibody 1 was used was there a linear correlation between the maximal transport rates of hexoses in BBMVs and the relative protein amounts determined by Western blot. These results indicate that the Na+-D-glucose cotransport in the jejunum, the ileum, and the rectum of chickens is due to an SGLT-1 type protein.

Animals↗
PubMed1999

Regulation of L-methionine and L-lysine uptake in chicken jejunal brush-border membrane by dietary methionine.

In the chicken intestine, L-methionine is transported by systems that are specific for neutral amino acids (L- and B-like) and by systems that can also transport cationic amino acids (y(+)m and b(0,+)-like). These four uptake pathways have been investigated in brush-border membrane vesicles from the jejunum of chickens fed a diet enriched with 0.4% L-methionine. Methionine supplementation from the 1st to the 6th wk of age has no effect on body weight or on the efficiency of food utilization. The kinetic analysis of L-methionine influx across the transport systems specific for neutral amino acids shows, for system L, no dietary effect on the Michaelis constant (Km) and a 30% reduction in maximal velocity (Vmax); for system B it shows a decrease in Km (30%) and in Vmax (51%). Transport systems shared by cationic and neutral amino acids show no dietary effect on b(0,+) activity and a significant reduction in y(+)m Vmax, similar for L-methionine and L-lysine, both in the absence and in the presence of Na+ (L-methionine, 30 and 26% reduction; L-lysine, 19 and 28% reduction, respectively). The downregulation induced by L-methionine supplementation may be an adaptive response to reduce the risk of intoxication by dietary excess of L-methionine. These results support the view that the toxicity of the supplemented substrate can be an important factor in the regulation of amino acid transport by dietary content.

Administration, Oral↗
PubMed1998

Effect of a lysine-enriched diet on L-lysine transport by the brush-border membrane of the chicken jejunum.

The influx of L-lysine into apical vesicles from the chicken jejunum occurs through two systems, one with low Michaelis constant (K(m)) and features of system b0,+ and the other with relatively high K(m) for L-lysine and with properties of system y+. In the present study the effect of a lysine-enriched diet (Lys, containing 68 g L-lysine/kg dietary protein, control animals 48 g/kg) on L-lysine uptake through both transport systems was investigated. Results show that 1) lysine enrichment had no effect on either body weight or the efficiency of food utilization. 2) In Lys-fed animals, the mediated L-lysine influx was best fitted to the two-system model with y+ and b0,+ activity. 3) In the presence of an Na+ gradient, total L-lysine uptake is significantly higher in Lys-fed animals than in control birds (about 40% increase). 4) Lys diet increases K(m)b0,+ 6-fold (KSCN gradient) and 12-fold (NaSCN gradient) and maximum velocity (Vmax) by 6- and 20-fold, respectively. The effects of Lys enrichment on the y(+)-like system are only observed on the Vmax and in the presence of a Na+ gradient (30% increase). 5) Na+ is involved in the activation of the transport process in the Lys-fed chickens, but there is no correlation between external Na+ concentration and L-lysine influx. In conclusion, both b(0,+)- and y(+)-like transport systems are upregulated by dietary lysine but with different kinetic profiles; the high-capacity y(+)-like carrier shows a Vmax increase without changes in K(m), whereas the low-capacity b(0,+)-like system shows an increase in Vmax as well as in the K(m).

Animals↗
PubMed1997

Transport of L-valine by the chicken caecum.

1. We have studied L-valine transport by the caecal segments of 6- to 8-week-old chickens. Isolated enterocytes from the proximal caecum incubated with 0.1 mM L-valine can accumulate the substrate against a concentration gradient. After 50 min incubation, the intracellular L-valine concentration reached 0.53 mM, a value higher than that observed in enterocytes from the jejunum (0.34 mM; P< 0.01). 2. Enterocytes from the medial and distal caccal regions are unable to transport L-valine uphill (cell concentration: 0.1 mM). 3. Amino acid accumulation by proximal caecal cells was Na+ -dependent and was inhibited by ouabain and 2,4-dinitrophenol. L-methionine inhibits L-valine uptake and a 2.5 mM concentration abolishes the capacity of enterocytes to accumulate the substrate. 4. The high accumulation ratios shown by the proximal caecum for L-valine suggest a role for this intestinal segment in the absorption of neutral amino acids present in the caecal chamber.

2,4-Dinitrophenol↗