Longitudinal outcomes of obeticholic acid therapy in ursodiol-nonresponsive primary biliary cholangitis: Stratifying the impact of add-on fibrates in real-world practice

BACKGROUND

Suboptimal response to ursodeoxycholic acid occurs in 40% of primary biliary cholangitis (PBC) patients, affecting survival. Achieving a deep response (normalisation of alkaline phosphatase [ALP] and bilirubin ≤0.6 upper limit of normal) improves survival. Yet, the long-term effectiveness of second-line treatments remains uncertain.

AIMS

To evaluate the long-term effectiveness of obeticholic acid (OCA) ± fibrates. Focusing on biochemical response (ALP ≤1.67 times the upper limit of normal, with a decrease of at least 15% from baseline and normal bilirubin levels), normalisation of ALP, deep response and biochemical remission (deep response plus aminotransferase normalisation).

METHODS

We conducted a longitudinal, observational, multicentre study involving ursodeoxyccholic acid non-responsive PBC patients (Paris-II criteria) from Spain and Portugal who received OCA ± fibrates.

RESULTS

Of 255 patients, median follow-up was 35.1 months (IQR: 20.2-53). The biochemical response in the whole cohort was 47.2%, 61.4% and 68.6% at 12, 24 and 36 months. GLOBE-PBC and 5-year UK-PBC scores improved (p < 0.001). Triple therapy (ursodeoxycholic acid plus OCA plus fibrates) had significantly higher response rates than dual therapy (p = 0.001), including ALP normalisation, deep response and biochemical remission (p < 0.001). In multivariate analysis, triple therapy remained independently associated with biochemical response (p = 0.024), alkaline phosphatase normalisation, deep response and biochemical remission (p < 0.001). Adverse effects occurred in 41.2% of cases, leading to 18.8% discontinuing OCA. Out of 55 patients with cirrhosis, 12 developed decompensation. All with baseline portal hypertension.

CONCLUSION

Triple therapy was superior in achieving therapeutic goals in UDCA-nonresponsive PBC. Decompensation was linked to pre-existing portal hypertension.

Are liver contour and bone fusion comparable to fiducials for IGRT in liver SBRT?

Introduction

Liver stereotactic body radiotherapy (SBRT) is increasingly being used to treat tumours. The purpose of this study was to compare the differences in patient positioning when using implanted fiducials as surrogates compared to alternative methods based on liver contour or bone registration.

Material and methods

Eighteen patients treated with SBRT who underwent a fiducial placement procedure were included. Fiducial guidance was our gold standard to guide treatment in this study. After recording the displacements, when fusing the planning CT and CBCT performed in the treatment unit using fiducials, liver contour and bone reference, the differences between fiducials and liver contour and bone reference were calculated. Data from 88 CBCT were analyzed. The correlation between the displacements found with fiducials and those performed based on the liver contour and the nearest bone structure as references was determined. The mean, median, variance, range and standard deviation of the displacements with each of the fusion methods were obtained. μ, Ʃ, and σ values and margins were obtained.

Results

Lateral displacements of less than 3 mm with respect to the gold standard in 92% vs. 62.5% of cases using liver contour and bone references, respectively, with 93.2% vs. 65.9% in the AP axis and SI movement in 69.3% vs. 51.1%. The errors μ, σ and Ʃ of the fusions with hepatic contour and bone reference in SI were 0.26 mm, 4 mm and 3 mm, and 0.8 mm, 5 mm and 3 mm respectively.

Conclusion

Our study showed that displacements were smaller with the use of hepatic contour compared to bone reference and comparable to those obtained with the use of fiducials in the lateral, AP and SI motion axes. This would justify that hepatic contouring can be a guide in the treatment of patients in the absence of fiducials.

Pre-surgical risk assessment in patients with cirrhosis

Over the last decades, significant improvements in the clini- cal management of patients with cirrhosis have increased their life expectancy. Thus, indications for surgical procedures other than liver transplantation are becoming more frequent. However, patients with advanced liver disease are at high risk of perioperative morbidity and mortality. This is the consequence of multiple factors that include the presence of portal hypertension, alterations on hemostasis and coagulation, the immune dysfunction that entails an increased risk of infections, and the impaired synthesis of proteins that impacts on the nutritional status and the wound healing. Surgical outcomes are not only determined by the severity of the liver disease, but also by the type of surgery and the presence of other comorbidities. Different models to predict mortality have been proposed, including the MELD score, the Child-Pugh classification, the hepatic venous pressure gradient, and the Mayo postoperative mortality risk calculator, among others. Multidisciplinary committees including surgeons, anesthesiologists, hepatologists, critical care physicians and other specialties involved in each case, should assess individually the risk-benefit of the surgical procedure, also considering patient`s expectations and will.

Nadolol plus isosorbide mononitrate alone or associated with band ligation in the prevention of recurrent bleeding: a multicentre randomised controlled trial

BACKGROUND AND AIMS

Previous clinical trials suggest that adding non-selective beta-blockers improves the efficacy of endoscopic band ligation (EBL) in the prevention of recurrent bleeding, but no study has evaluated whether EBL improves the efficacy of beta-blockers + isosorbide-5-mononitrate. The present study was aimed at evaluating this issue in a multicentre randomised controlled trial (RCT) and to correlate changes in hepatic venous pressure gradient (HVPG) during treatment with clinical outcomes

METHODS

158 patients with cirrhosis, admitted because of variceal bleeding, were randomised to receive nadolol+isosorbide-5-mononitrate alone (Drug: n = 78) or combined with EBL (Drug+EBL; n = 80). HVPG measurements were performed at randomisation and after 4-6 weeks on medical therapy.

RESULTS

Median follow-up was 15 months. One-year probability of recurrent bleeding was similar in both groups (33% vs 26%: p = 0.3). There were no significant differences in survival or need of rescue shunts. Overall adverse events or those requiring hospital admission were significantly more frequent in the Drug+EBL group. Recurrent bleeding was significantly more frequent in HVPG non-responders than in responders (HVPG reduction >or=20% or <or=12 mm Hg). Among non-responders recurrent bleeding was similar in patients treated with Drugs or Drugs+EBL.

CONCLUSIONS

Adding EBL to pharmacological treatment did not reduce recurrent bleeding, the need for rescue therapy, or mortality, and was associated with more adverse events. Furthermore, associating EBL to drug therapy did not reduce the high rebleeding risk of HVPG non-responders. ISRCTN26221020.

Endoscopic follow-up of gastric ulcer in a population at intermediate risk for gastric cancer

OBJECTIVES

Primary: to assess the necessity of a second endoscopy with a pathology study to confirm the healing of all gastric ulcers previously diagnosed through endoscopy in a population at intermediate risk for gastric cancer. Secondary: to assess correlation between endoscopic findings and pathology diagnosis.

PATIENTS AND METHODS

a prospective analysis of patients diagnosed with gastric ulcer through endoscopy at Hospital General de Ciudad Real (Spain) over three years. We collected demographic, clinical, endoscopic, and pathological data for the first and subsequent endoscopies. We collected at least six biopsies obtained from ulcer margins, and assessed H. pylori infection.

RESULTS

Three hundred and two patients were included in this study. H. pylori infection was diagnosed in 173 (57%), and 113 (37%) patients had used NSAIDs. The positive and negative predictive value for malignancy of endoscopic diagnosis regarding ulcer fold, base, and margins were 34 and 97%, respectively. Only one patient was diagnosed with a tumor during the second endoscopy. At the end of follow-up, the etiology of the ulcer was considered as peptic in 276 patients; Crohn s disease-related in one, and neoplastic in 25 patients (21 adenocarcinomas, 4 lymphomas).

CONCLUSIONS

in an intermediate-risk population for gastric cancer a second endoscopy is not justified for gastric ulcer patients when endoscopy and biopsy results do not suggest malignancy.

[Hepatitis C virus in populations at risk for infection. Venezuela]

OBJECTIVE

The aim of this study was to establish the prevalence of hepatitis C virus infection in different populations at risk for infection.

METHODS

This was a descriptive, transversal study whose variables were evaluated by Pearson s correlation analysis. Different populations were selected: 100 drug users, 47 sex workers, and 50 hemodialysis patients for a total of 197 individuals. The only inclusion criterion was the apparent risk of acquiring this viral infection. The presence of antibodies against virus was examined by ELISA IV (Innotest HCV Ab IV). Reactive samples were then tested using a recombinant assay (INNO-LIA HCV Ab III), both from Innogenetics N. V. (Belgium). The presence of viral RNA was determined in all ELISA and immunoblot-reactive samples by a nested polymerase chain reaction method (HCV-fast of Pharma Gen).

RESULTS

A prevalence of 1% was found in drug users, and absence of infection or previous contact with the virus in sex workers and hemodialysis patients.

CONCLUSIONS

This study shows a very low prevalence of infection with hepatitis C virus in populations at risk for acquiring the infection, and considered that this infection is not a public health problem in these populations in Maracaibo, Venezuela.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Sustained response to interferon-alpha or to interferon-alpha plus ribavirin in hepatitis C virus-associated symptomatic mixed cryoglobulinaemia

BACKGROUND

Hepatitis C virus (HCV) infection has been associated with mixed cryoglobulinaemia.

AIM

To investigate the efficacy of anti-viral therapy on the eradication of HCV and its clinical manifestations in patients with HCV-associated symptomatic mixed cryoglobulinaemia.

PATIENTS AND METHODS

18 out of 32 patients with symptomatic mixed cryoglobulinaemia (MC group) received a 12-month course of interferon (3 MU three times a week, subcutaneously). Nonresponders or relapsers to this therapy were treated with interferon plus ribavirin (1200 mg/day, orally) for 12-months. 226 patients with HCV infection and without cryoglobulins were studied in comparison (Hepatitis C group). Serial quantification of serum HCV-RNA and cryoglobulins were performed.

RESULTS

In the MC group, 10 out of 18 patients (55%) receiving interferon showed an end of treatment response, but at the end of follow-up, only five (28%) patients had a sustained response. In the hepatitis C group, 91 patients (47%) showed an end of treatment response but only 42 (20%) a sustained response. In the MC group alanine transaminase, cryocrit and rheumatoid factor decreased significantly in responders, with an improvement or disappearance of the MC-associated clinical manifestations. Alanine transaminase, cryocrit and rheumatoid factor increased in the relapsers and the clinical manifestations reappeared. Nonresponders and relapsers to interferon in the MC group were retreated with interferon plus ribavirin. Five out of eight nonresponders showed a end of treatment response but it was sustained in three of them. In the relapsers, treatment with combined therapy achieved a sustained response in four out of the five patients (80%).

CONCLUSIONS

Interferon as monotherapy or combined with ribavirin is a safe and effective treatment in patients with HCV-associated MC. The presence of cryoglobulins does not affect the response to anti-viral treatment in patients with HCV infection. The eradication of HCV is associated with an improvement or disappearance of MC-associated clinical manifestations.

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.

Factors mediating the hemodynamic effects of tumor necrosis factor-alpha in portal hypertensive rats

Nitric oxide, prostacyclin, and glucagon have been implicated in promoting the hyperdynamic circulatory state of portal hypertension. Recent evidence also indicates that increased tumor necrosis factor-alpha (TNF-alpha) production is involved in the pathogenesis of this hemodynamic abnormality. This study was aimed at investigating in rats with portal vein stenosis (PVS) the effects on splanchnic hemodynamics of blocking circulating TNF-alpha and the factors mediating the vascular action of this cytokine in this setting. Anti-TNF-alpha polyclonal antibodies or placebo was injected into rats (n = 96) before and 4 days after PVS (short-term inhibition) and at 24 h and 4, 7, 10 days after PVS (long-term inhibition). Short-term TNF-alpha inhibition reduced portal venous inflow and cardiac index and increased splanchnic and systemic resistance. Portal pressure was unchanged, but portal-systemic shunting was decreased. After long-term TNF-alpha inhibition, portal venous inflow and portal pressure were unchanged, but arterial pressure and systemic resistance rose significantly. Anti-TNF-alpha PVS rats exhibited lower increments of systemic resistance after Nomega-nitro-L-arginine methyl ester and indomethacin administration and lower serum levels of TNF-alpha, nitrates-nitrites, and 6-keto-PGF1alpha, both over the short and the long term. Serum glucagon levels rose after long-term inhibition. In conclusion, the specific role played by TNF-alpha in the development of the hyperdynamic state of portal hypertension appears to be mainly mediated through an increased release of nitric oxide and prostacyclin. Maintenance of the splanchnic hyperemia after long-term TNF-alpha inhibition could be due to a compensatory release of glucagon.

Randomized controlled trial of sclerotherapy versus somatostatin infusion in the prevention of early rebleeding following acute variceal hemorrhage in patients with cirrhosis. Variceal Bleeding Study Group

BACKGROUND/AIMS

Early rebleeding is a very frequent complication of variceal hemorrhage. Sclerotherapy effectively controls variceal hemorrhage and prevents early rebleeding. Somatostatin infusion is as effective as sclerotherapy in controlling variceal hemorrhage, but no study has evaluated the efficacy of 5-day somatostatin infusion in preventing early rebleeding after the initial control of bleeding. The aim of the study was to compare the efficacy and safety of somatostatin and sclerotherapy in the prevention of early variceal rebleeding in cirrhotic patients.

METHODS

The study included 169 patients with acute variceal hemorrhage who were randomized within 24 h of controlling the acute bleeding to receive either sclerotherapy (n=79) or continuous somatostatin infusion for 5 days (250 microg/h after a 250-microg bolus, repeated every 24 h, n=90). Success of therapy was defined by absence of rebleeding during the 5 days following randomization.

RESULTS

Early (5 days) rebleeding occurred in 12/79 patients treated with sclerotherapy vs 14/90 of those receiving somatostatin (NS). The treatment was equally effective in Child's C patients (sclerotherapy: 18/20; somatostatin: 17/20; NS) and Child's A+B patients (sclerotherapy: 49/59; somatostatin: 59/70; NS). Complications occurred in 19/79 patients receiving sclerotherapy vs 4/90 in the somatostatin group (p= 0.00019), being severe in 6 vs 0 patients (p=0.0094). There were no differences between the two groups in the incidence of 6-week rebleeding (14% vs 15%, NS) and mortality (9% vs 9%).

CONCLUSIONS

Continuous somatostatin infusion is as effective as sclerotherapy in preventing early variceal rebleeding and maintaining low mortality following acute variceal hemorrhage. Somatostatin is associated with a lower rate of complications than sclerotherapy.

[Evaluation of the hemodynamic effects of tumor necrosis factor alpha factor in rats with portal hypertension using the radioactive microsphere technique]

This study was aimed at investigating the effects of blocking circulating TNF on the hyperdynamic circulatory state developed in rats with portal vein stenosis (PVS), and the factors mediating the hemodynamic action of this cytokine in this setting.

MATERIALS AND METHODS

Murine antiTNF polyclonal antibodies (100 microgram) or placebo were intravenously injected into PVS rats (n = 24) before and 4 days after PVS. Hemodynamic studies were performed the day after the last antiTNF injection.

RESULTS

Short-term TNF inhibition led to reductions in cardiac index (p < 0.05) and portal venous inflow (p < 0.01), and significant increases in splanchnic and systemic vascular resistances. Portal pressure was unchanged, but portal-systemic shunting was decreased (p < 0.05).

CONCLUSION

TNF plays a key role in promoting the development of the hyperdynamic state of portal hypertension. The effect of TNF is mediated through an increased release of nitric oxide.

Propranolol plus prazosin compared with propranolol plus isosorbide-5-mononitrate in the treatment of portal hypertension

BACKGROUND & AIMS

The association of prazosin to propranolol enhances the decrease in portal pressure but may cause hypotension and sodium retention. The aim of this study was to compare the portal pressure reduction and safety of the combination of propranolol plus prazosin with that of propranolol plus isosorbide-5-mononitrate (ISMN).

METHODS

Fifty-six portal-hypertensive cirrhotics received randomly propranolol plus prazosin (n = 28) or propranolol plus ISMN (n = 28) orally for 3 months. Hemodynamics and liver and renal function were assessed at baseline and after 3 months.

RESULTS

Propranolol plus prazosin caused a greater reduction in hepatic venous pressure gradient (HVPG) than propranolol plus ISMN (-24.2% +/- 11% vs. -16.1% +/- 11%; P < 0.01). A reduction in HVPG of > 20% was significantly more frequent in the propranolol plus prazosin group than in the propranolol plus ISMN group (85% vs. 53%; P < 0.05). Neither treatment modified hepatic blood flow, quantitative liver function test results, glomerular filtration rate, plasma renin activity, or plasma aldosterone level. Side effects occurred in 13 patients receiving propranolol plus prazosin compared with 7 receiving propranolol plus ISMN (P = 0.16).

CONCLUSIONS

Propranolol plus prazosin has a greater portal pressure-lowering effect than propranolol plus ISMN. Both therapies were safe for liver and renal function. However, the combination of propranolol plus prazosin caused a greater decrease in arterial pressure and was less well tolerated than propranolol plus ISMN.

Selective impairment of endothelium-mediated vasodilation in liver transplant recipients with cyclosporin A-induced hypertension

Arterial hypertension is commonly observed in orthotopic liver transplantation (OLT) recipients receiving cyclosporin A (CsA), but the precise pathogenetic mechanisms remain partially unknown. The aim of this study was to investigate endothelium-dependent and -independent dilation and adrenergic constriction of resistance vessels of OLT recipients treated with CsA. Vascular reactivity was examined in 22 OLT patients, 10 with and 12 without arterial hypertension, and in 10 control subjects by assessing the forearm blood flow response to the brachial artery infusion of increasing concentrations of methacholine chloride, sodium nitroprusside, and phenylephrine. In 10 OLT patients, the response to methacholine was also examined after acetylsalicylate. The ratio of serum nitrite and nitrate to serum creatinine was lower (P < .05) in OLT patients with hypertension than in nonhypertensive patients and controls. Basal forearm flow was similar in the three groups. Methacholine vasodilation was impaired in the hypertensive patients as shown by a lower maximum forearm vasodilator response and a shift in the dose response curve to methacholine to the right compared with the nonhypertensive OLT patients and the controls. The response to methacholine was not modified after salicylate. Forearm flow response to nitroprusside was similar in the three groups. No differences between the patients and the controls were found in the maximum forearm flow contraction in response to phenylephrine. An impairment in endothelium-dependent vasodilation could mediate arterial hypertension in OLT patients immunosuppressed with CsA.

Analogies and differences between omega-conotoxins MVIIC and MVIID: binding sites and functions in bovine chromaffin cells

The characteristics of the binding sites for the Conus magus toxins omega-conotoxin MVIIC and omega-conotoxin MVIID, as well as their effects on K+-evoked 45Ca2+ entry and whole-cell Ba2+ currents (IBa), and K+-evoked catecholamine secretion have been studied in bovine adrenal chromaffin cells. Binding of [125I] omega-conotoxin GVIA to bovine adrenal medullary membranes was displaced by omega-conotoxins GVIA, MVIIC and MVIID with IC50 values of around 0.1, 4 and 100 nM, respectively. The reverse was true for the binding of [125I] omega-conotoxin MVIIC, which was displaced by omega-conotoxins MVIIC, MVIID and GVIA with IC50 values of around 30, 80 and 1.200 nM, respectively. The sites recognized by omega-conotoxins MVIIC and MVIID in bovine brain exhibited higher affinities (IC50 values of around 1 nM). Both omega-conotoxin MVIIC and MVIID blocked IBa by 70-80%; the higher the [Ba2+]o of the extracellular solution the lower the blockade induced by omega-conotoxin MVIIC. This was not the case for omega-conotoxin MVIID; high Ba2+ (10 mM) slowed down the development of blockade but the maximum blockade achieved was similar to that obtained in 2 mM Ba2+. A further difference between the two toxins concerns their reversibility; washout of omega-conotoxin MVIIC did not reverse the blockade of IBa while in the case of omega-conotoxin MVIID a partial, quick recovery of current was produced. This component was irreversibly blocked by omega-conotoxin GVIA, suggesting that it is associated with N-type Ca2+ channels. Blockade of K+-evoked 45Ca2+ entry produced results which paralleled those obtained by measuring IBa. Thus, 1 microM of each of omega-conotoxin GVIA and MVIIA inhibited Ca2+ uptake by 25%, while 1 microM of each of omega-conotoxin MVIIC and MVIID caused a 70% blockade. K+-evoked catecholamine secretory responses were not reduced by omega-conotoxin GVIA (1 microM). In contrast, at 1 microM both omega-conotoxin MVIIC and MVIID reduced the exocytotic response by 70%. These data strengthen the previously established conclusion that Q-type Ca2+ channels that contribute to the regulation of secretion and are sensitive to omega-conotoxins MVIIC and MVIID are present in bovine chromaffin cells. These channels, however, seem to possess binding sites for omega-conotoxins MVIIC and MVIID whose characteristics differ considerably from those described to occur in the brain; they might represent a subset of Q-type Ca2+ channels or an entirely new subtype of voltage-dependent high-threshold Ca2+ channel.

The exocytotic event in chromaffin cells revealed by patch amperometry

In mast cells and granulocytes, exocytosis starts with the formation of a fusion pore. It has been suggested that neurotransmitters may be released through such a narrow pore without full fusion. However, owing to the small size of the secretory vesicles containing neurotransmitter, the properties of the fusion pore formed during Ca2+-dependent exocytosis and its role in transmitter release are still unknown. Here we investigate exocytosis of individual chromaffin granules by using cell-attached capacitance measurements combined with electrochemical detection of catecholamines, achieved by inserting a carbon-fibre electrode into the patch pipette. This allows the simultaneous determination of the opening of individual fusion pores and of the kinetics of catecholamine release from the same vesicle. We found that the fusion-pore diameter stays at <3 nm for a variable period, which can last for several seconds, before it expands. Transmitter is released much faster through this pore than in mast cells, generating a 'foot' signals which precedes the amperometric spike. Occasionally, the narrow pore forms only transiently and does not expand, allowing complete transmitter release without full fusion of the vesicle with the plasma membrane.

Accuracy of portal and forearm blood flow measurements in the assessment of the portal pressure response to propranolol

BACKGROUND/AIMS

The portal pressure response to propranolol varies significantly in individual patients with cirrhosis. At present, propranolol responders can be identified only by measuring the hepatic venous pressure gradient. The aims of this study were: 1) to investigate whether the noninvasive monitoring of portal blood flow by pulsed Doppler ultrasound and forearm blood flow by strain-gauge plethysmography can predict the hepatic venous pressure gradient response to propranolol in patients with cirrhosis, and 2) to analyze the factors that may influence this response.

METHODS

Hemodynamic measurements were undertaken in 80 patients with cirrhosis before and after receiving propranolol (0.15 mg/kg i.v., n = 60) or placebo (n = 20).

RESULTS

No changes were observed in the placebo group. Propranolol lowered (p < 0.01) hepatic venous pressure gradient from 17.6 +/- 3.8 to 14.7 +/- 3.8 mmHg, portal blood flow from 1122 +/- 363 to 897 +/- 332 ml/min and forearm blood flow from 7.52 +/- 3.1 to 6.12 +/- 2.3 ml/min%. Changes in hepatic venous pressure gradient were correlated (p < 0.01) with those of portal blood flow (r = 0.82) and forearm blood flow (r = 0.54). The reduction in hepatic venous pressure gradient was > 20% in 23 patients ("responders"). The accuracy of portal Doppler flowmetry in identifying responders was higher than that of forearm plethysmography (88.3 vs. 68.3%, p < 0.05). Multivariate analysis proved that previous variceal bleeding was the only factor independently associated with a lack of response to propranolol (relative risk 3.42, 95% CI 1.5-7.4, p < 0.01). Hepatic venous pressure gradient reduction by propranolol was higher in non-bleeders than in bleeders (-19.9 +/- 9.4 vs. -11.3 +/- 8.6%, p < 0.01).

CONCLUSIONS

Portal Doppler ultrasound can be used as a reliable surrogate indicator of the hepatic venous pressure gradient response to acute propranolol administration. In addition, our study indicates that this response is mainly influenced by previous variceal hemorrhage.

Changes in gastrin and serum pepsinogens in monitoring of Helicobacter pylori response to therapy

The aims of this study in 50 patients with H. pylori infection and duodenal ulcer were to examine the effect of eradication therapy on the serum levels of gastrin, pepsinogen I, and pepsinogen II and to investigate whether monitoring of the serum changes in these peptides after treatment could predict patient outcome. H. pylori status was assessed at entry and one and six months after therapy by culturing and microscopic analysis of the gastric mucosa and by [14C]urea breath test. Significant decreases were observed in the serum levels of gastrin (-11.4 +/- 3%), pepsinogen I (-28.9 +/- 4%), and pepsinogen II (-40.4 +/- 3%) in the 45 patients whose infection was eradicated, but not in the patients without eradication. Serum values of these peptides were unchanged in an additional group of 10 patients that only received omeprazol, none of whom had H. pylori eradicated. The best cutoff point of the percentage of each peptide to predict patient outcome was 10% for gastrin and pepsinogen I, and 15% for pepsinogen II. A pepsinogen II decrease > 15% resulted in the best marker of H. pylori clearance, accurately identifying patient outcome 86.6% of the time, whereas the diagnostic accuracy of gastrin and pepsinogen I was 61.7% and 76.6%, respectively. Significant correlations were found between the bacterial load assessed by histology with the serum concentrations of pepsinogen I and II and with the urease activity as measured by the amount of 14CO2 excreted. In conclusion, eradication of H. pylori infection is followed by a significant drop in serum levels of gastrin, pepsinogen I, and pepsinogen II. Changes in the latter are the most uniform and may be used as an indirect tool to predict treatment outcome.

omega-Conotoxins block neurotransmission in the rat vas deferens by binding to different presynaptic sites on the N-type Ca2+ channel

Electrically-induced twitch responses of the prostatic segment of vas deferens (0.1 Hz, 65 V, 1 ms) are mainly due to the transient presynaptic release of ATP, which acts postsynaptically on non-adrenergic receptors to contract smooth muscle cells. These responses were fully blocked by nanomolar concentrations of the omega-conotoxins GVIA, MVIIA, and MVIIC, most likely by inhibiting Ca2+ entry through presynaptic N-type Ca2+ channels controlling the release of ATP. Repeated washout of the toxins allowed the recovery of contractions, except for omega-conotoxin GVIA, whose inhibitory effects remained unchanged for at least 60 min. In addition, micromolar concentrations of omega-conotoxin MVIIC were unable to protect against the irreversible inhibition of twitch contractions induced by nanomolar concentrations of omega-conotoxin GVIA. At low extracellular Ca2+ concentrations (1.5 mM), 20 nM of omega-conotoxin GVIA or MVIIA inhibited completely the twitch contractions in about 10 min. In 5 mM Ca2+ the blockade of twitch contractions after 10 min was 70% for both toxins. In 1.5 mM Ca2+ omega-conotoxin MVIIC (1 microM) inhibited completely the twitch contraction after 10 min. In 5 mM Ca2+ blockade developed very slowly and was very poor after 30 min, omega-conotoxin MVIIC depressed the response by only 20%. These results are compatible with the idea that the three omega-conotoxins block the purinergic neurotransmission of the vas deferens by acting on presynaptic N-type voltage-dependent Ca2+ channels. However, omega-conotoxin MVIIC seems to bind to sites different from those recognised by omega-conotoxin GVIA and MVIIA, which are markedly differentiated by their Ca2+ requirements for binding to their receptors.

Re-evaluation of the P/Q Ca2+ channel components of Ba2+ currents in bovine chromaffin cells superfused with solutions containing low and high Ba2+ concentrations

This study was undertaken to reassess the set of voltage-dependent Ca2+ channel subtypes expressed by bovine adrenal chromaffin cells maintained in primary cultures. Previous views on the pharmacology of such channels had to be revised in the light of the novel data which arose from the use in this study of low and high micromolar concentrations of omega-agatoxin IVA, and low (2 mM) and high (10 mM) concentrations of the charge carrier Ba2+. Whole-cell Ba2+ currents (IBa) through Ca2+ channels were elicited in voltage-clamped chromaffin cells, with a holding potential of -80 mV and depolarising pulses to 0 mV. Mean peak IBa was 425 pA in 2 mM Ba2+ (59 cells) and 787 pA in 10 mM Ba2+ (42 cells). In 2 mM Ba2+, omega-conotoxin MVIIC (3 microM) inhibited IBa by 79%; in 10 mM Ba2+, the blockade developed much more slowly and reached only 44%. A low concentration of omega-agatoxin IVA (20 nM) inhibited IBa by 9%; 2 microM inhibited IBa by 60%. This blockade was similar in low and high Ba2+ concentrations. After giving furnidipine (3 microM) and omega-conotoxin GVIA (1 microM), 2 microM omega-agatoxin IVA inhibited the remaining current (about 40-45%); this blockade was independent of the Ba2+ concentration. The current could be fully blocked by the cocktail furnidipine/omega-conotoxin GVIA/high omega-agatoxin IVA, both in low and high Ba2+ concentrations. The large Q-type channel component of IBa is blocked by micromolar concentrations of omega-agatoxin IVA and omega-conotoxin MVIIC. While solutions with a high Ba2+ concentration strongly delayed the development of blockade by omega-conotoxin MVIIC, the blockade by high concentrations of omega-agatoxin IVA was equally effective in solutions with a low or a high Ba2+ concentration. Hence, the use of appropriate Ba2+ and toxin concentrations in this study reveals that P-type Ca2+ channels are poorly expressed in bovine chromaffin cells; in contrast, a robust component of the current depends on Q-type Ca2+ channels. An R-type residual current is not present in these cells.

Opioid inhibition of Ca2+ channel subtypes in bovine chromaffin cells: selectivity of action and voltage-dependence

Bovine chromaffin cells possess a mixture of high-voltage-activated Ca2+ channel subtypes: L-type, dihydropyridine-sensitive channels, and N-, P- and Q-types, omega-conotoxin MVIIC-sensitive channels. In these cells, we studied the reversible, naloxone-antagonized inhibition of Ba2+ currents by the opioid agonist met-enkephalin (IC50 = 272 nM). This inhibition could be resolved into a voltage-dependent and a voltage-independent component. The first was revealed by its slow Ba2+ current activation kinetics at 0 mV and by the current facilitation induced by short prepulses to +90 mV. The second was estimated as the residual inhibition persisting after the facilitation protocol. The two inhibitory components varied markedly from cell to cell and each contributed to about half of the total inhibition. Replacement of internal GTP by GDP-beta-S or cell pretreatment with pertussis toxin completely abolished the voltage-dependent inhibition by opioids, partially preserving the voltage-independent component. The opioid-induced inhibition was not selective for any Ca2+ channel subtype, being not prevented after the addition of specific Ca2+ channel antagonists. However, when separately analysing the contribution of each channel type to the voltage-dependent and voltage-independent modulation, a clear-cut distinction could be achieved. The voltage-independent inhibition was effective on all Ca2+ channel subtypes but predominantly on L-type Ca2+ channels. The voltage-dependent process was abolished by omega-conotoxin-MVIIC, but unaffected by nifedipine, and was thus sharply restricted to non-L-type channels (N-, P- and Q-types). Our data suggest a functionally distinct opioid receptor-mediated modulation of L- and non-L-type channels, i.e. of the two channel classes sharing major control of catecholamine secretion from bovine chromaffin cells.

The mechanism of calcium channel facilitation in bovine chromaffin cells

1. This study was planned to clarify the mechanism of Ca2+ channel facilitation by depolarizing prepulses given to voltage-clamped bovine chromaffin cells. The hypothesis for an autocrine modulation of such channels was tested by studying the effects of a soluble vesicle lysate (SVL) on whole-cell Ba2+ currents (IBa). 2. SVL was prepared from a bovine adrenal medullary homogenate. The ATP content in this concentrated SVL amounted to 3.18 +/- 0.12 mM (n = 4). The concentration of noradrenaline and adrenaline present in the SVL was 11.2 +/- 0.97 and 15.2 +/- 2 mM, respectively (n = 5). A 1:1000 dilution of SVL in the external solution halved the magnitude of IBa and produced a 7-fold slowing of its activation kinetics. The blocking effects of SVL were concentration dependent and quickly reversed upon washout. 3. Inhibition and slowing of the kinetics of IBa by SVL could be partially reversed by strong depolarizing prepulses (+90 mV, 45 ms). This reversal of inhibition, called Ca2+ channel facilitation, persisted in the presence of 3 microM nifedipine. 4. Intracellular dialysis of GDP-beta-S (0.5 mM) or pretreatment of the cells with pertussis toxin (100 ng ml-1 for 18-24 h) prevented the reduction in peak current caused by a 1:100 dilution of SVL; no prepulse facilitation could be observed under these conditions. 5. The receptor blockers naloxone (10 microM) or suramin (100 microM) and PPADS (100 microM) largely antagonized the effects of SVL. Treatment of SVL with alkaline phosphatase or dialysis against a saline buffer to remove low molecular mass materials (< 10 kDa) considerably reduced the activity of SVL. 6. Stopping the flow of the external solution (10 mM Ba2+) gradually reduced the size, and slowed down the activation phase, of the current. Prepulse facilitation of IBa was absent or weak in a superfused cell, but was massive upon flow-stop conditions in the presence or absence of 3 microM nifedipine. 7. Our experiments suggest that facilitation by prepulses of whole-cell current through Ca2+ channels is due to the suppression of an autoinhibitory autocrine loop present in bovine chromaffin cells. By acting at least on purinergic and opiate receptors, the exocytotic release of ATP and opiates will cause a tonic inhibition of the current through a G-protein-mediated mechanism. Such a mechanism will be removed by strong depolarizing prepulses, and will involve preferentially non-L-type channels. In the light of these and other recent results, previously held views on the selective recruitment by prepulses of dihydropyridine-sensitive Ca2+ channels are not tenable.