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Biomedical subjects

A Albillos

Publications and source records attributed to A Albillos.

At least 19 recordsLinked to original sources
PubMed2004

Mitochondrial calcium sequestration and protein kinase C cooperate in the regulation of cortical F-actin disassembly and secretion in bovine chromaffin cells.

Mitochondria play an important role in the homeostasis of intracellular Ca(2+) and regulate its availability for exocytosis. Inhibitors of mitochondria Ca(2+) uptake such as protonophore CCCP potentiate the secretory response to a depolarizing pulse of K(+). Exposure of cells to agents that directly (cytochalasin D, latrunculin B) or indirectly (PMA) disrupt cortical F-actin networks also potentiate the secretory response to high K(+). The effects of cytochalasin D and CCCP on secretion were additive whereas those of PMA and CCCP were not; this suggests different mechanisms for cytochalasin D and CCCP and a similar mechanism for PMA and CCCP. Mitochondria were the site of action of CCCP, because the potentiation of secretion by CCCP was observed even after depletion of Ca(2+) from the endoplasmic reticulum. CCCP induced a small increase in the cytosolic Ca(2+) concentration ([Ca(2+)](c)) that was not modified by the protein kinase C (PKC) inhibitor chelerythrine. Both CCCP and PMA induced cortical F-actin disassembly, an effect abolished by chelerythrine. In addition, rotenone and oligomycin A, two other mitochondrial inhibitors, also evoked cortical F-actin disassembly and potentiated secretion; again, these effects were blocked by chelerythrine. CCCP also enhanced the phosphorylation of PKC and myristoylated alanine-rich C kinase substance (MARCKS), and these were also inhibited by chelerythrine. The results suggest that the rapid sequestration of Ca(2+) by mitochondria would protect the cell from an enhanced PKC activation and cortical F-actin disassembly, thereby limiting the magnitude of the secretory response.

Actins↗
PubMed2001

Multicenter randomized controlled trial comparing different schedules of somatostatin in the treatment of acute variceal bleeding.

BACKGROUND/AIMS: The dose of somatostatin used for variceal bleeding (250 microg/h) is lower than that proven to effectively decrease portal pressure and azygos blood flow (500 microg/h). Moreover, i.v. somatostatin boluses have greater effects than continuous infusions. The aim of this study was to investigate whether higher doses of somatostatin and repeated boluses may increase its efficacy in controlling variceal bleeding. METHODS: A total of 174 patients with acute variceal bleeding were randomized to receive for 48 h: (A) one 250 microg bolus +250 microg/h infusion; (B) three 250 microg boluses +250 microg/h infusion; (C) three 250 microg boluses +500 microg/h infusion. RESULTS: The three schedules of somatostatin were equally effective in controlling variceal bleeding (73, 75 and 81%, respectively, NS). Multivariate analysis showed active bleeding at endoscopy (n=75) as the only predictor of failure to control bleeding. In these patients, the 500 microg/h infusion dose achieved a higher rate of control of bleeding (82 vs. 60%, P<0.05), less transfusions (3.7 +/- 2.7 vs. 2.5 +/- 2.3 UU, P=0.07) and better survival (93 vs. 70%, P<0.05) than schedules A/B. CONCLUSIONS: Somatostatin is highly effective in controlling variceal bleeding. Patients with active bleeding at emergency endoscopy may benefit from higher doses of somatostatin infusion.

Acute Disease↗
PubMed2001

Control of secretion by mitochondria depends on the size of the local [Ca2+] after chromaffin cell stimulation.

In chromaffin cells, plasma membrane calcium (Ca2+) channels and mitochondria constitute defined functional units controlling the availability of Ca2+ nearby exocytotic sites. We show here that, when L-/N-type Ca2+ channels were inhibited with nisoldipine and omega-conotoxin GVIA, cytosolic [Ca2+] ([Ca2+]c) peaks measured in fura-4F-loaded cells were reduced by 36%; however, mitochondrial Ca2+ uptake was unaffected and secretion was potentiated by protonophores as in control cells. By contrast, when non L-type Ca2+ channels were inhibited with omega-conotoxin MVIIC, [Ca2+]c peaks induced by high K+ were reduced by 73%, mitochondrial Ca2+ uptake was abolished, and secretion was not modified by protonophores. However, if Ca2+ entered only through L-type channels activated by FPL64176, high K+ stimulation induced fast mitochondrial Ca2+ uptake and catecholamine secretion was strongly increased and potentiated by protonophores. These results confirm the close association of catecholamine secretion to mitochondrial Ca2+ uptake, and indicate the sharp threshold of local [Ca2+]c (about 5 microM) required for triggering fast mitochondrial Ca2+ uptake that is able to modulate secretion. The entry of Ca2+ through L-type channels generated local [Ca2+]c increases just below that, inducing little mitochondrial Ca2+ uptake unless FPL64176 was present. By contrast, Ca2+ entry through P/Q-type channels fully activated mitochondrial Ca2+ uptake. Control of secretion by mitochondria therefore depends critically on the ability of the stimulus to create large local [Ca2+]c microdomains.

Adrenal Medulla↗
PubMed2001

Time course of serum hepatitis C virus-RNA during chronic hepatitis C treatment accurately predicts the type of response.

AIM: To establish the value of alanine aminotransferase normalization and hepatitis C virus-RNA clearance as predictors of sustained virological response in naïve and relapser chronic hepatitis C patients on mono or combination therapy. METHODS: A total of 282 hepatitis C patients were studied: 98 naïves on interferon, and 64 naïves and 75 relapsers on interferon plus oral ribavirin; 45 patients were excluded. Drugs were administered at standard doses for 12 months. Alanine aminotransferase and hepatitis C virus-RNA were determined at baseline and at weeks 4, 12, 24, 48, and at 72 and 96 weeks after completion of therapy. RESULTS: The rate of sustained response was greater (P < 0.05) in naïves and relapsers on combination therapy (33% and 48%, respectively) than in naïves on interferon alone (16%). Hepatitis C virus-RNA significantly decreased from baseline by week 4 in naïves on interferon and relapsers on combination therapy and by week 12 in naïves on combination therapy. Alanine aminotransferase levels paralleled viremic load in naïves on interferon, yet in patients on combination therapy, alanine aminotransferase normalized independently of the virological response. During treatment, the main factor associated with sustained response was hepatitis C virus-RNA clearance by week 4 in naïves on interferon and relapsers on combination therapy, and by week 24 in naïves on combination therapy. CONCLUSION: Clearance of viraemia constitutes the best predictor of a sustained response to therapy, but needs to be measured at patient-specific times.

Adult↗
PubMed2001

Randomized comparison of long-term losartan versus propranolol in lowering portal pressure in cirrhosis.

BACKGROUND & AIMS: It has been suggested that losartan, an angiotensin II (A-II) type 1 receptor blocker, may have a pronounced portal pressure reducing effect, far greater than that of propranolol. This randomized controlled trial compared the hemodynamic and renal effects of continued 6-week administration of losartan (n = 25) vs. propranolol (n = 15) in portal hypertensive patients with cirrhosis treated endoscopically after a variceal bleeding episode. METHODS: Hepatic venous pressure gradient (HVPG), systemic hemodynamics, renal function, and vasoactive factors were measured before and at 6 weeks of treatment. RESULTS: Losartan did not reduce HVPG (-2% +/- 12%, NS) but significantly decreased mean arterial pressure (MAP, -8% +/- 10%, P = 0.001). On the contrary, propranolol significantly reduced HVPG (-10% +/- 11%, P = 0.003) and cardiac output (-16% +/- 12%, P = 0.001) but did not modify MAP (2.5% +/- 10%, NS). Losartan increased A-II levels, reduced aldosterone, and decreased glomerular filtration rate (GFR) in Child B patients. Propranolol did not modify renal function. Adverse events related to therapy were mild and similar in both groups. CONCLUSIONS: Unlike propranolol, long-term losartan administration does not significantly reduce HVPG in patients with cirrhosis treated after a variceal bleeding episode, and it caused hypotension and reduced GFR in patients with moderate liver failure. Therefore, losartan is not an alternative to propranolol in preventing variceal rebleeding.

Adult↗
PubMed2001

Mitochondrial Ca(2+)-induced Ca(2+) release mediated by the Ca(2+) uniporter.

We have reported that a population of chromaffin cell mitochondria takes up large amounts of Ca(2+) during cell stimulation. The present study focuses on the pathways for mitochondrial Ca(2+) efflux. Treatment with protonophores before cell stimulation abolished mitochondrial Ca(2+) uptake and increased the cytosolic [Ca(2+)] ([Ca(2+)](c)) peak induced by the stimulus. Instead, when protonophores were added after cell stimulation, they did not modify [Ca(2+)](c) kinetics and inhibited Ca(2+) release from Ca(2+)-loaded mitochondria. This effect was due to inhibition of mitochondrial Na(+)/Ca(2+) exchange, because blocking this system with CGP37157 produced no further effect. Increasing extramitochondrial [Ca(2+)](c) triggered fast Ca(2+) release from these depolarized Ca(2+)-loaded mitochondria, both in intact or permeabilized cells. These effects of protonophores were mimicked by valinomycin, but not by nigericin. The observed mitochondrial Ca(2+)-induced Ca(2+) release response was insensitive to cyclosporin A and CGP37157 but fully blocked by ruthenium red, suggesting that it may be mediated by reversal of the Ca(2+) uniporter. This novel kind of mitochondrial Ca(2+)-induced Ca(2+) release might contribute to Ca(2+) clearance from mitochondria that become depolarized during Ca(2+) overload.

Aequorin↗
PubMed2001

Isosorbide mononitrate in the prevention of first variceal bleed in patients who cannot receive beta-blockers.

BACKGROUND & AIMS: Nonselective beta-blockers (beta-blockers) are very effective in preventing first variceal bleeding (FVB) in patients with cirrhosis. However, 15%-25% of patients have contraindications or develop severe side effects precluding its use. The present study evaluates whether isosorbide-5-mononitrate (Is-MN) effectively prevents variceal bleeding in patients with contraindications or who could not tolerate beta-blockers. METHODS: One hundred thirty-three consecutive cirrhotic patients with gastro-esophageal varices and contraindications or intolerance to beta-blockers were included in a multicenter, prospective, double-blind randomized controlled trial. Sixty-seven were randomized to receive Is-MN, and 66 to receive placebo. RESULTS: There were no significant differences in the 1- and 2-year actuarial probability of experiencing a FVB between the 2 treatment groups. Presence of variceal red signs at endoscopy was the only variable independently associated with an increased risk of variceal bleeding on follow-up (relative risk 3.4; P < 0.01). Survival and adverse events were similar in the 2 groups. There were no significant differences in the incidence of ascites or changes in renal function. CONCLUSIONS: Is-MN does not reduce the incidence of FVB in patients with cirrhosis and esophageal varices who cannot be treated with beta-blockers because contraindications or intolerance to these drugs, suggesting that Is-MN has no place in the primary prophylaxis of variceal bleeding.

Adrenergic beta-Antagonists↗
PubMed2000

R-Type Ca2+ channels are coupled to the rapid component of secretion in mouse adrenal slice chromaffin cells.

Patch-clamp measurements of Ca(2+) currents and membrane capacitance were performed on slices of mouse adrenal glands, using the perforated-patch configuration of the patch-clamp technique. These recording conditions are much closer to the in vivo situation than those used so far in most electrophysiological studies in adrenal chromaffin cells (isolated cells maintained in culture and whole-cell configuration). We observed profound discrepancies in the quantities of Ca(2+) channel subtypes (P-, Q-, N-, and L-type Ca(2+) channels) described for isolated mouse chromaffin cells maintained in culture. Differences with respect to previous studies may be attributable not only to culture conditions, but also to the patch-clamp configuration used. Our experiments revealed the presence of a Ca(2+) channel subtype never before described in chromaffin cells, a toxin and dihydropyridine-resistant Ca(2+) channel with fast inactivation kinetics, similar to the R-type Ca(2+) channel described in neurons. This channel contributes 22% to the total Ca(2+) current and controls 55% of the rapid secretory response evoked by short depolarizing pulses. Our results indicate that R-type Ca(2+) channels are in close proximity with the exocytotic machinery to rapidly regulate the secretory process.

Adrenal Glands↗
PubMed2000

Greater diversity than previously thought of chromaffin cell Ca2+ channels, derived from mRNA identification studies.

Using reverse transcription followed by PCR amplification (RT-PCR), we have identified multiple messenger RNAs encoding for the neuronal pore-forming Ca(2+) channel subunits alpha(1A) (P/Q channel), alpha(1B) (N channel), alpha(1D) (neuronal/endocrine L channel), alpha(1E) (R channel), alpha(1G-H) (T channel) and alpha(1S) (skeletal muscle L channel) in bovine chromaffin cells. mRNAs for the auxiliary beta(2), beta(3), beta(4), alpha(2)/delta and gamma(2) subunits were also identified. In agreement with these molecular data, perforated patch-clamp recordings of whole-cell Ca(2+) currents reveal the existence of functional R-type Ca(2+) channels in these cells that were previously undetected with other techniques. Our results provide a molecular frame for a much wider functional diversity of Ca(2+) channels in chromaffin cells than that previously established using pharmacological and electrophysiological approaches.

Animals↗
PubMed2000

Effect of propranolol on the factors promoting bacterial translocation in cirrhotic rats with ascites.

Bacterial translocation appears to be an important mechanism in the pathogenesis of spontaneous infections in cirrhosis. Cirrhotic patients are commonly treated with beta-adrenoceptor blockers, but the impact of this treatment in the factors promoting bacterial translocation has not been investigated. This study was aimed at investigating in cirrhotic rats with ascites the effect of propranolol on intestinal bacterial load, transit, and permeability of the bowel and on the rate of bacterial translocation. Bacterial translocation to mesenteric lymph nodes and intestinal bacterial overgrowth, permeability (urinary excretion of (99m)Tc-diethylenetriaminepentaacetic acid [(99m)Tc-DTPA]), and transit (geometric center ratio of (51)Cr) were assessed in 29 rats with carbon tetrachloride (CCl(4)) cirrhosis and 20 controls. These variables were then measured in 12 placebo- and in 13 propranolol-treated ascitic cirrhotic rats. Bacterial translocation was present in 48% of the cirrhotic rats and in none of the controls. Cirrhotic rats with intestinal bacterial overgrowth had a significantly higher rate of translocation and slower intestinal transit than those without it. Among the 15 rats with overgrowth and a (99m)Tc-DTPA excretion greater than 10%, 15 had translocation and 2 had bacterial peritonitis. Only 1 of the 14 rats with either intestinal overgrowth or a (99m)Tc-DTPA excretion greater than 10% presented translocation. Compared with the placebo group, propranolol-treated animals had significantly lower portal pressure, faster intestinal transit, and lower rates of bacterial overgrowth and translocation. In ascitic cirrhotic rats, bacterial translocation results from intestinal overgrowth and severe damage to gut permeability. In this setting, intestinal overgrowth is associated with intestinal hypomotility. Propranolol accelerates the intestinal transit, decreasing the rates of bacterial overgrowth and translocation.

Animals↗
PubMed2000

Altered regulation of calcium channels and exocytosis in single human pheochromocytoma cells.

We established primary cultures of human pheochromocytoma chromaffin cells. We then tried to find what mechanism of their secretory apparatus could be altered to produce the massive release of catecholamines into the circulation and the subsequent hypertensive crisis observed in patients suffering this type of tumor. Their whole-cell Ca2+ channel currents could be pharmacologically separated into components similar to those found in normal human adrenal chromaffin cells: 20% L-type, 30% N-type, and 50% P/Q-type Ca2+ channels. However, modulation of the channels by exogenous or endogenous ATP and opioids, via a G-protein membrane-delimited pathway, was deeply altered; some cells having no modulation or very little modulation alternated with others having normal modulation. This may be the cause of the uncontrolled secretory response, measured amperometrically at the single-cell level. Some cells secreted for long time periods and were insensitive to nifedipine (L-type channel blocker) or to omega-conotoxin MVIIC (N/P/Q-type channel blocker), while others were highly sensitive to nifedipine and partially sensitive to omega-conotoxin MVIIC. Alteration of the autocrine/paracrine modulation of Ca2+ channels may lead to indiscriminate Ca2+ entry and exacerbate catecholamine release responses in human pheochromocytoma cells.

Adenosine Triphosphate↗
PubMed2000

Chromaffin-cell stimulation triggers fast millimolar mitochondrial Ca2+ transients that modulate secretion.

Activation of calcium-ion (Ca2+) channels on the plasma membrane and on intracellular Ca2+ stores, such as the endoplasmic reticulum, generates local transient increases in the cytosolic Ca2+ concentration that induce Ca2+ uptake by neighbouring mitochondria. Here, by using mitochondrially targeted aequorin proteins with different Ca2+ affinities, we show that half of the chromaffin-cell mitochondria exhibit surprisingly rapid millimolar Ca2+ transients upon stimulation of cells with acetylcholine, caffeine or high concentrations of potassium ions. Our results show a tight functional coupling of voltage-dependent Ca2+ channels on the plasma membrane, ryanodine receptors on the endoplasmic reticulum, and mitochondria. Cell stimulation generates localized Ca2+ transients, with Ca2+ concentrations above 20-40 microM, at these functional units. Protonophores abolish mitochondrial Ca2+ uptake and increase stimulated secretion of catecholamines by three- to fivefold. These results indicate that mitochondria modulate secretion by controlling the availability of Ca2+ for exocytosis.

Acetylcholine↗
PubMed2000

Multicenter randomized controlled trial of terlipressin versus sclerotherapy in the treatment of acute variceal bleeding: the TEST study.

Failure to control bleeding and early rebleeding account for the high mortality associated with variceal hemorrhage in cirrhosis. We compared endoscopic sclerotherapy to terlipressin, a drug that effectively controls acute bleeding while reducing in-hospital mortality. This multicenter randomized controlled trial included 219 cirrhotic patients admitted for endoscopy-proven acute variceal bleeding and randomized to receive repeated injections of terlipressin during 6 days (n = 105) or emergency sclerotherapy (n = 114). Success was defined as obtaining control of bleeding (24-hour bleeding-free period during the first 48 hours) and lack of early rebleeding (any further bleeding from initial control to 5 days later) and survival during the study. Both groups were similar at inclusion. Failure rate for terlipressin was 33% and 32% for sclerotherapy (not significant [NS]). Early rebleeding was responsible for 43% and 44% of failures, respectively. This high efficacy was observed in both Child-Pugh class A + B and Child-Pugh class C patients. Both treatments were similar regarding transfusion requirements, in-hospital stay, and 6-week mortality (26 vs. 19 patients). Side effects appeared in 20% of patients receiving terlipressin and in 30% of those on sclerotherapy (P =.06); being serious in 4% and 7%, respectively (NS). In conclusion, terlipressin and sclerotherapy are equally highly effective therapies achieving the initial control of variceal bleeding and preventing early rebleeding. Both treatments are safe, but terlipressin is better tolerated. Therefore, terlipressin may represent a first-line treatment in acute variceal bleeding until the administration of elective therapy, especially in hospitals where a skilled endoscopist is not available 24 hours a day.

Acute Disease↗
PubMed1999

A preferential pole for exocytosis in cultured chromaffin cells revealed by confocal microscopy.

Histological studies suggest that adrenal medulla chromaffin cells in situ are polarised, but functional evidence is lacking. We present here the first demonstration for polarisation of exocytosis in isolated, spherical, bovine chromaffin cells. Cells were stimulated with 70 mM K(+) to cause a marked enhancement of catecholamine release, monitored amperometrically. FM1-43 and dopamine beta-hydroxylase antibodies provided fluorescence confocal pictures that were 2-3-fold more intense in the bottom of the cells, as compared to equatorial or apex planes. This suggests that the solid phase to which the cell attaches serves as a 'trophic' signal for the polarisation of its secretory apparatus.

Animals↗
PubMed1999

Improvement in liver fibrosis, functionality and hemodynamics in CCI4-cirrhotic rats after injection of the Liver Growth Factor.

BACKGROUND/AIMS: Most substances used in experimental models of cirrhosis are chosen either as protectors of lipid peroxidation, as antifibrogenic agents or as vitamins, among others. In this report, we analyze the improvement produced, in established cirrhosis (CCl4 plus phenobarbital) in rats, by intraperitoneal injection of Liver Growth Factor, a hepatic mitogen with activity both in vivo and in vitro. METHODS: Following confirmation of CCl4-induced cirrhosis, Liver Growth Factor (4.5 microg per ratx2 injections/week for 3 weeks) was administered to one group of rats (Cirr+LGF). The remaining rats (Cirr) received saline. The groups were compared in terms of serum enzymes, tissue damage, total liver collagen, collagenase activity, microsomal enzyme activities, splanchnic and systemic hemodynamics and portosystemic shunting. RESULTS: Treatment of rats presenting CCl4-induced cirrhosis with Liver Growth Factor decreased serum aminotransferase levels and increased levels of serum albumin and total protein. The Liver collagen content was lower in rats treated with Liver Growth Factor (2.96 vs. 4.32 mg/g liver, p<0.01). Microscopic studies revealed that the livers of rats receiving Liver Growth Factor showed decreases in fibrosis, necrosis and inflammatory infiltration, as well as a recovery of architectural integrity. Liver function was improved after treatment with Liver Growth Factor, as indicated by the rate constant for elimination of aminopyrine, which increased from 0.0063 to 0.0170 (p<0.05). This increase was accompanied by a higher total amount of cytochrome P-450 as well as of certain P-450 isoenzymes, especially those that are hormone-dependent, such as P-450 3A. The improved liver histology and function observed in Cirr+LGF rats was associated with decreases in portal pressure (14.4 vs. 9.4 mm Hg, p<0.01) and portosystemic shunting (55.8 vs. 11.5%, p<0.01), as well as increases in mean arterial pressure and systemic vascular resistance, and a reduction in ascites. CONCLUSIONS: Administration of the hepatic mitogen, Liver Growth Factor, to CCl4-cirrhotic rats decreased liver collagen and reorganized the hepatic extracellular matrix, resulting in an improvement in liver function, reduced portal pressure and amelioration of ascites.

Aminopyrine↗