Modulatory Role of Vitamin E on Proton Pump (ATPase) Activity of Cadmium Chloride-Induced Testicular Damage in Wistar Rats

Proton pumps are membrane-bound enzymes important in generating gradients that help in maintaining cellular ion homeostasis, cell membrane potential, water, and solute transport across the cell surface. This study investigated the modulatory role of vitamin E on proton pump activity and reproductive parameters in cadmium-induced testicular damage. Twenty (20) male Wistar rats weighing between 180 and 200 g were sorted into 4 groups of five rats each. Group I served as the control and was given normal saline orally, Group II rats were treated with a single dose of 2 mg/kg BW cadmium chloride (CdCl2) intraperitoneally, Group III rats were given 100 mg/kg BW of vitamin E orally, and Group IV rats were given 100 mg/kg BW of vitamin E orally for 30 days prior to intraperitoneal administration of single dose of 2 mg/kg BW of cadmium chloride. The rats were anaesthetized with diethyl ether, and blood samples were obtained for sex hormonal analysis; caudal epididymis was dissected for sperm count, motility, and viability, and the testis were homogenized for lipid peroxidation and proton pump (Na+/K+ ATPase, Ca2+ ATPase, and Mg2+ ATPase) activity. Proton pump activity was assayed spectrophotometrically using the Stewart method to determine the inorganic phosphate level. Histopathological changes of the testis were also studied. The group treated with CdCl2 showed a significant (p < 0.05) decrease in proton pump activity, sperm count, and motility and a significant (p < 0.05) increase in malondialdehyde level when compared with the control group. The CdCl2-treated group also showed decrease reproductive organ weights and hormonal levels and cause necrosis of spermatogonia lining the seminiferous tubules. Rats treated with vitamin E orally for 30 days prior to CdCl2 exposure showed improvement in proton pump activity, a significant (p < 0.05) increase in sperm parameters and luteinizing hormonal level, and a decrease in the lipid peroxidation level as compared with the CdCl2 group. This study showed that vitamin E ameliorated the toxic effect of CdCl2 on proton pump activity in the testes, hence improving testicular integrity, structures, and functions.

Functional complexes of the proton pump and chloride transporter in gastric acid secretion

Proton(H+) of gastric acid(HCl) is actively secreted by gastric proton pump (H+, K+- ATPase) in the parietal cells. The proton pump is expressed in both tubulovesicles and apical membrane of the cells. In resting parietal cells, tubulovesicles are present in intracellular compartments underlying the apical membrane and forming a reticulated meshwork. Upon stimulation, tubulovesicles fuse each other and connect with the apical membrane, resulting in massive acid secretion. On the other hand, the mechanism of apical Cl- transport for HCl secretion is not fully understood, although several Cl- transporters and Cl- channels have been reported to be the candidate. Here, we summarized the function of Cl- transporters such as KCC4, a K+-Cl- cotransporter, and ClC-5, a Cl-/H+ exchanger, in gastric acid secretion.

[Effects of exogenous spermidine on lipid peroxidation and membrane proton pump activity of cucumber seedling leaves under high temperature stress]

Taking a relatively heat-resistant cucumber (Cucumis sativus) cultivar 'Jinchun No. 4' as test material, a sand culture experiment was conducted in growth chamber to investigate the effects of foliar spraying spermidine (Spd) on the lipid peroxidation, membrane proton pump activity, and corresponding gene expression of cucumber seedling leaves under high temperature stress. Compared with the control, foliar spraying Spd increased the plant height, stem diameter, dry and fresh mass, and leaf area significantly, and inhibited the increase of leaf relative conductivity, malondialdehyde (MDA) content, and lipoxygenase (LOX) activity effectively. Foliar spraying Spd also helped to the increase of leaf plasma membrane- and tonoplast H(+)-ATPase activity, but no significant difference was observed in the gene expression levels. These results suggested that exogenous Spd could significantly decrease the leaf lipid peroxidation and increase the proton pump activity, and thus, stabilize the leaf membrane structure and function, alleviate the damage induced by high temperature stress, and enhance the heat tolerance of cucumber seedlings.

Comparison of heavy metal effect on the proton pumps of plasma membrane and tonoplast in cucumber root cells

The effects of 10 microM cadmium, copper and nickel on the activities of vacuolar membrane and plasma membrane (PM) ATP-dependent proton pumps was investigated in Cucumis sativus L. root cells. It was demonstrated that vacuolar H+-ATPase (EC 3.6.3.14) and PM H+-ATPase (EC 3.6.3.6) differed in sensitivity to heavy metals. Exposure of cucumber seedlings to Cd, Cu and Ni had no significant effect on the activity of the vacuolar proton pump and, in the case of Ni, also on the activity of the PM proton pump. In contrast, Cd and Cu ions diminished both ATP hydrolysis and proton transport in plasma membranes. Transcript levels of genes encoding PM enzyme as well as the subunit A of tonoplast enzyme in roots stressed with heavy metals were similar to the control. Cd, Cu and Ni were accumulated in cucumber roots with similar efficiency, but their relative distribution between the symplast and apoplast differed. To explain the mechanism of heavy metal action on the plasma membranes of cucumber roots, the MDA content, as a lipid peroxidation product, and fatty acid composition were analyzed. It was shown that exposure of plants to Cd, Cu and Ni did not enhance the lipid peroxidation in the PM fraction. However, all metals caused an increase in the saturation of PM fatty acids and a decrease in the length of the fatty acid chain.

Preparation of tetrahydroimidazo[2,1-a]isoquinolines and their use as inhibitors of gastric acid secretion

A series of novel tetrahydroimidazo[2,1-a]isoquinolines was prepared based on a hetero Diels-Alder reaction between an enamine and 1,2,4-triazine as key step. A structure-activity relationship was established focussing on the influence of the substitution pattern in position 3 and 6 of the heterocycle on antisecretory activity, lipophilicity, and pK(a) value. Potent inhibitors of the gastric acid pump were identified.

Glycocardiolipin modulates the surface interaction of the proton pumped by bacteriorhodopsin in purple membrane preparations

Glycocardiolipin is an archaeal analogue of mitochondrial cardiolipin, having an extraordinary affinity for bacteriorhodopsin, the photoactivated proton pump in the purple membrane of Halobacterium salinarum. Here purple membranes have been isolated by osmotic shock from either cells or envelopes of Hbt. salinarum. We show that purple membranes isolated from envelopes have a lower content of glycocardiolipin than standard purple membranes isolated from cells. The properties of bacteriorhodopsin in the two different purple membrane preparations are compared; although some differences in the absorption spectrum and the kinetic of the dark adaptation process are present, the reduction of native membrane glycocardiolipin content does not significantly affect the photocycle (M-intermediate rise and decay) as well as proton pumping of bacteriorhodopsin. However, interaction of the pumped proton with the membrane surface and its equilibration with the aqueous bulk phase are altered.

[Basic diagnostic methods in gastro-esophageal reflux disease]

Gastro-esopgageal reflux disease (GERD) incidence increase in most developed countries. It concerns 5 to 15% of the population. It requuires life style modification as well as prolonged medicamentd intake. The current situation requires development of new techniques of diagnosing and treatment as well as enhancement of old ones. The effective care of the patient suffering from GERD requires interdisciplinary cooperation. It means general practicioner, gastroenterologist, diatary specialist and sometimes psychologist and recently more commonly surgeon. Despite development of new dianostic methods still basic medical care should be based on anamnesis, physical assessment, endoscopic and radiological procedures. Other methods are designed to treat more complicated or associated with the higher risk of complication manifestations of GERD. Still individual assessment is of all given results allow the proper choice of proceeding and method of treatment. Ph-metry and manometry of esophagus or nowadays more commonly used ph-metry with impedancy and its combination with manometry does not answer all the diagnostic questions. Authors present possibilities and limitations of basic diagnostic methods used in GERD.

[Endoscopic methods of gastro-esophageal reflux disease (GERD) treatment and their complications]

Tretament in gastro-esophageal reflux disease (GERD) is in constant change. It is caused by the fact of change and development of diagnostic and therapeutic methods. Alternative methods of treatment are still searched beacause patients do not accept many years long drug treatment or surgical procedures. New methods are developed. Some of them as endoscopic fundoplication or methods of polimerizing substances injection in the area of lower esophageal sphincer have been abandoned because of low quickly diminishing efficacy Endoscopic sewing that implicate all layers of gaster is still under clinical trials and is considered as interesting. Stertt's procedure that is based on electromagnetic wave application in the area of lower esophageal sphincter is used in clinical practice. Despite effective methods of diagnosing and treatment of GERD there is no evidence of lowering incidence of complications of GERD. It is still common to find esophagus stricture as the first illness manifastation. Chronic character of GERD is associated with intestinal metaplasia and adenocarcinoma of the esophagus in its distal part. The most effective endoscopic methods of the treatment include: endoscopic dilation of the strictures and endoscopic methods of patological epithelium removal in Barrett's esophagus. These are: photodynamic therapy, argon coagulation, laser thermoablation, multipolar ablation and endoscpic mucosectomy. The paper is the review of the methods aimed at GERD and its complication treatment.

Is there any acid peptic disease that is refractory to proton pump inhibitors?

Non-healing and delayed healing during acid inhibition treatment depend on the extent to which acid and 'non-acid' factors are causative in the particular acid peptic disease, and on the effectiveness and duration of acid suppression. Refractoriness (defined arbitrarily) occurs less often with proton pump inhibitors than with H2-receptor antagonists as the former decrease acid more effectively; H2-receptor antagonist-refractory disease usually responds to treatment with proton pump inhibitors. In Rotherham, 5-10% of duodenal ulcer and gastric ulcer patients are refractory (not healed after > or = 3 months of standard-dose H2-receptor antagonist). In patients with oesophagitis 15% are refractory to high-dose H2-receptor antagonist (for example, 3.2 g cimetidine daily) and 5% to standard-dose proton pump inhibitors (for example, 20 mg omeprazole daily). In controlled clinical trials of patients with refractory duodenal ulcer, healing at 8 weeks with 40 mg omeprazole o.m. vs. continued standard-dose H2-receptor antagonist was 98% vs. 60%; and with 40 mg omeprazole vs. continued high-dose H2-receptor antagonist (2 g + 3 g cimetidine, that is, ultra-refractory disease) was 92% vs. 67%. After healing, in open studies, relapse with maintenance 400-800 mg cimetidine nocte was 45-69% at one year, but 0% with 40 mg omeprazole administered for up to 6.5 years. For 53 patients with refractory gastric ulcer, in an open study, healing with omeprazole 40 mg o.m. occurred in 94% at 8 weeks, and none relapsed on long-term maintenance treatment at this dose. In controlled trials of patients with refractory oesophagitis, healing at 12 weeks with 40 mg omeprazole o.m. vs. high-dose ranitidine (300 mg b.d.) was 90% vs. 47%, and with maintenance 20 mg omeprazole o.m. vs. 150 mg ranitidine b.d., relapse at 1 year was 32% vs. 88%. In conclusion, acid peptic disease refractory to H2-receptor antagonists is uncommon and treatment with proton pump inhibitors is effective. Refractoriness to proton pump inhibitors is rare.

Future prospects for proton pump inhibitors

Future prospects for proton pump inhibitors depend on their efficacy and safety relative to H2-receptor antagonists, the therapeutic standard for acid peptic disorders. As safety concerns diminish, efficacy considerations become more important as these may pertain to cost effectiveness. Comparative, controlled trials show that omeprazole and lansoprazole are somewhat more effective than H2-blockers in healing duodenal and gastric ulcers, providing faster relief of symptoms. Relapse after cessation of therapy is similar between the two classes. The proton pump inhibitors are substantially more effective in healing lesions and relieving symptoms in patients with reflux oesophagitis, and are particularly effective in cases that have failed to heal after 12 weeks of treatment with H2-blockers. Relapse rates of oesophagitis are significantly less with prolonged treatment with omeprazole than ranitidine. A proton pump inhibitor combined with amoxicillin is less effective than triple therapy with antibiotics and bismuth in eradicating Helicobacter pylori infections, but is more convenient and associated with fewer side-effects. Efficacy might be improved by more optimal dosing regimens. Prospects for reversible proton pump inhibitors depend on the balance between their theoretical advantages and their acid inhibition profile which, at present, closely resembles that of H2-blockers.

Proton pump inhibitors, enterochromaffin-like cell growth and Helicobacter pylori gastritis

In both rodents and humans the development of gastrin-promoted gastric argyrophil enterochromaffin-like cell carcinoids requires the involvement of a genetic factor inherent to multiple endocrine neoplasia syndrome or of type A autoimmune chronic atrophic gastritis. Prolonged severe hypergastrinaemia acting on non-gastritic mucosa, as in Zollinger-Ellison syndrome patients, results in diffuse argyrophil enterochromaffin-like cell hyperplasia but, as a rule, does not produce tumours. Combination of chronic atrophic gastritis (mostly related to Helicobacter pylori infection) with hypergastrinaemia frequently causes linear and micronodular hyperplasia of argyrophil cells, whereas carcinoids are exceptional. No tumours or pre-neoplastic lesions have been observed in patients treated long-term with proton pump inhibitors, apart from rare cases in patients with combined Zollinger-Ellison and multiple endocrine neoplasia syndromes. A moderate increase in the incidence of argyrophil cell clustering, with or without hyperplasia, probably results from the parallel evolution of ulcer-associated Helicobacter gastritis into chronic atrophic gastritis. Eradication of H. pylori with a combination of proton pump inhibitors and antibiotics suppresses gastritis and prevents ulcer recurrence.

Polyamines as physiological regulators of 14-3-3 interaction with the plant plasma membrane H+-ATPase

Polyamines are abundant polycationic compounds involved in many plant physiological processes such as cell division, dormancy breaking, plant morphogenesis and response to environmental stresses. In this study, we investigated the possible role of these polycations in modulating the association of 14-3-3 proteins with the H(+)-ATPase. In vivo experiments demonstrate that, among the different polyamines, spermine brings about 2-fold stimulation of the H(+)-ATPase activity and this effect is due to an increase in 14-3-3 levels associated with the enzyme. In vivo administration of polyamine synthesis inhibitors causes a small but statistically significant decrease of the H(+)-ATPase phosphohydrolytic activity, demonstrating a physiological role for the polyamines in regulating the enzyme activity. Spermine stimulates the activity of the H(+)-ATPase AHA1 expressed in yeast, in the presence of exogenous 14-3-3 proteins, with a calculated S(50) of 70 microM. Moreover, spermine enhances the in vitro interaction of 14-3-3 proteins with the H(+)-ATPase and notably induces 14-3-3 association with the unphosphorylated C-terminal domain of the proton pump. Comparison of spermine with Mg(2+), necessary for binding of 14-3-3 proteins to different target proteins, shows that the polyamine effect is stronger than and additive to that of the divalent cation.

The inhibitory binding site(s) of Zn2+in cytochromecoxidase

EXAFS analysis of Zn binding site(s) in bovine-heart cytochrome c oxidase and characterization of the inhibitory effect of internal zinc on respiratory activity and proton pumping of the liposome reconstituted oxidase are presented. EXAFS identifies tetrahedral coordination site(s) for Zn(2+) with two N-histidine imidazoles, one N-histidine imidazol or N-lysine and one O-COOH (glutamate or aspartate), possibly located at the entry site of the proton conducting D pathway in the oxidase and involved in inhibition of the oxygen reduction catalysis and proton pumping by internally trapped zinc.

Nonsteroidal anti-inflammatory drugs (NSAIDs), cyxlooxygenase-2 selective inhibitors (coxibs) and gastrointestinal harm: review of clinical trials and clinical practice

Background

Gastrointestinal harm, known to occur with NSAIDs, is thought to be lower with NSAID and gastroprotective agent, and with inhibitors selective to cyclooxygenase-2 (coxibs) at usual plasma concentrations. We examine competing strategies for available evidence of reduced gastrointestinal bleeding in clinical trials and combine this evidence with evidence from clinical practice on whether the strategies work in the real world, whether guidance on appropriate prescribing is followed, and whether patients adhere to the strategies.

Methods

We used a series of systematic literature searches to find full publications of relevant studies for evidence about the efficacy of these different gastroprotection strategies in clinical trials, and for evidence that they worked and were adhered to in clinical practice – whether they were effective. We chose to use good quality systematic reviews and meta-analyses when they were available.

Results

Evidence of efficacy of coxibs compared to NSAIDs for upper gastrointestinal bleeding was strong, with consistent reductions in events of about 50% in large randomised trials (34,460 patients), meta-analyses of randomised trials (52,474 patients), and large observational studies in clinical practice (3,093 bleeding events). Evidence on the efficacy of NSAID plus gastroprotection with acid suppressants (proton pump inhibitors, PPIs, and histamine antagonists, H2As) was based mainly on the surrogate measure of endoscopic ulcers. The limited information on damage to the bowel suggested that NSAID plus PPI was more damaging than coxibs.

Eleven observational studies studied 1.6 million patients, of whom 911,000 were NSAID users, and showed that 76% (range 65% to 90%) of patients with at least one gastrointestinal risk factor received no prescription for gastroprotective agent with an NSAID. The exception was a cohort of US veterans with previous gastrointestinal bleeding, where 75% had gastroprotection with an NSAID. When gastroprotection was prescribed, it was often described as inadequate. A single study suggested that patient adherence to prescribed gastroprotection was low.

Conclusion

Evidence for efficacy of gastroprotection strategies with NSAIDs is limited. In clinical practice few patients who need gastroprotection get it, and those who get it may not take it. For coxibs, gastroprotection is inherent, although probably not complete.

Probing conformations of the beta subunit of F0F1-ATP synthase in catalysis

A subcomplex of F0F1-ATP synthase (F0F1), alpha3beta3gamma, was shown to undergo the conformation(s) during ATP hydrolysis in which two of the three beta subunits have the "Closed" conformation simultaneously (CC conformation) [S.P. Tsunoda, E. Muneyuki, T. Amano, M. Yoshida, H. Noji, Cross-linking of two beta subunits in the closed conformation in F1-ATPase, J. Biol. Chem. 274 (1999) 5701-5706]. This was examined by the inter-subunit disulfide cross-linking between two mutant beta(I386C)s that was formed readily only when the enzyme was in the CC conformation. Here, we adopted the same method for the holoenzyme F0F1 from Bacillus PS3 and found that the CC conformation was generated during ATP hydrolysis but barely during ATP synthesis. The experiments using F0F1 with the epsilon subunit lacking C-terminal helices further suggest that this difference is related to dynamic nature of the epsilon subunit and that ATP synthesis is accelerated when it takes the pathway involving the CC conformation.

Dilated intercellular spaces: extending the reach of the endoscope

Two manuscripts in this issue utilize quantitative methods to analyze the association between gastroesophageal reflux disease (GERD) and dilated intercellular spaces (DIS) evident on transmission electron microscopy of the esophageal epithelium. One study of 20 patients found that, irrespective of whether or not a pH study was positive, all GERD patients who had responded to proton pump inhibitors therapy had intercellular space measurements that were at least twice normal. The other study demonstrated that DIS resolved with effective GERD therapy in essentially every instance. Both studies suggest that DIS are an objective structural marker of endoscopy-negative reflux disease.

Kinetics and control of oxidative phosphorylation in rat liver mitochondria after dexamethasone treatment

The present investigation was undertaken in order to evaluate the contributions of ATP synthesis and proton leak reactions to the rate of active respiration of liver mitochondria, which is altered following dexamethasone treatment (1.5 mg/kg per day for 5 days). We applied top-down metabolic control analysis and its extension, elasticity analysis, to gain insight into the mechanisms of glucocorticoid regulation of mitochondrial bioenergetics. Liver mitochondria were isolated from dexamethasone-treated, pair-fed and control rats when in a fed or overnight fasted state. Injection of dexamethasone for 5 days resulted in an increase in the fraction of the proton cycle of phosphorylating liver mitochondria, which was associated with a decrease in the efficiency of the mitochondrial oxidative phosphorylation process in liver. This increase in proton leak activity occurred with little change in the mitochondrial membrane potential, despite a significant decrease in the rate of oxidative phosphorylation. Regulation analysis indicates that mitochondrial membrane potential homoeostasis is achieved by equal inhibition of the mitochondrial substrate oxidation and phosphorylation reactions in rats given dexamethasone. Our results also suggest that active liver mitochondria from dexamethasone-treated rats are capable of maintaining phosphorylation flux for cellular purposes, despite an increase in the energetic cost of mitochondrial ATP production due to increased basal proton permeability of the inner membrane. They also provide a complete description of the effects of dexamethasone treatment on liver mitochondrial bioenergetics.

Investigation of the contribution of histidine 119 to the conduction of protons through human Nox2

The conduction of protons through human Nox2 has previously been shown to be dependent upon His115. Alignment of sequences for both animal and plant Nox proteins indicated that histidines 115 and 119 are both highly conserved, while His111 was conserved among animal homologues of Nox1-4. To investigate the possible role that these histidine residues might play in the conduction of protons through Nox2, we have introduced both paired and single mutations into these histidine residues. Each construct was used to generate a CHO cell line in which the expression of the mutated Nox2 was assessed. Nox2 was expressed in each of the CHO cell lines generated, however, the level of expression of H111/115L in CHO cells was lower and that of H111L very much reduced, compared to that of wild-type Nox2. The arachidonic acid activated proton flux was absent in the CHO cell lines expressing the mutations of H111/115L, H111/119L or H115/119L, compared to that observed for wild-type Nox2. Similarly only a small efflux of protons was observed from CHO cells expressing either H119L or H111L. In all cases the expected proton flux was elicited through the addition of the protonophore, carbonyl cyanide m-chlorophenylhydrazone. Conclusions regarding the role of His111 in the conduction of protons cannot be drawn due to the reduced expression. We can, however, conclude that His119, in addition to His115, is required for the conduction of protons through Nox2. His119 has been identified as a highly conserved residue for which no function has previously been proposed.

Spatial coordination of chloroplast and plasma membrane activities in Chara cells and its disruption through inactivation of 14-3-3 proteins

In Chara corallina cells exposed to continuous light, external pH (pH(o)) and photosystem II (PSII) photochemical yield show correlated banding patterns. Photosynthetic activity is low in cell regions producing alkaline zones and high in the acid regions. We addressed the question whether (and how) photosynthetic activity and plasma membrane (PM) H+-pumping and H+-conductance are coupled in the different bands. First, PM H+-pump activity was stimulated with fusicoccin. This resulted in a more acidic pH in the acid bands without disturbing the correlation of photosynthetic electron transport and H+ fluxes across the PM. Next, H+-pump activity was reduced through microinjection of a phosphorylated peptide matching the canonical 14-3-3 binding motif RSTpSTP in the acid cell region. Microinjection induced a rapid (~5 min) rise in pH(o) by ca. 1.0 unit near the injection site, whereas the injection of the non-phosphorylated peptide had no effect. This pH rise confirms the supposed inhibition of the H+-pump upon the detachment of 14-3-3 proteins from the H+-ATPase. However, the PSII yield in the cell regions corresponding to the new alkaline peak remained high, which violated the normal inverse relations between the pH(o) and PSII photochemical yield. We conclude that the injection of the competitive inhibitor of the H+-ATPase disrupts the balanced operation of PM H+-transport and photosynthetic electron flow and promotes electron flow through alternative pathways.

Flagellar motors of marine bacteriaHalomonasare driven by both protons and sodium ions

Bacterial cells in aquatic environments are able to reach or stay near nutrient patches by using motility. Motility is usually attained by rotating flagellar motors that are energized by electrochemical potential of H+or Na+. In this paper, the ion specificity for flagellar rotation of two marine isolates Halomonas spp. strains US172 and US201 was investigated. Both isolates require sodium for growth and possess a respiratory-driven primary sodium pump. They are motile because of lateral flagella regardless of the presence of sodium ions. Their swimming speed under various concentrations of sodium ions with and without carbonylcyanide m-chlorophenylhydrazone, a proton conductor, and with and without phenamil, a specific inhibitor for the sodium-driven flagellar motors, was examined. The effect of carbonylcyanide m-chlorophenylhydrazone on the transmembrane proton gradient was also determined. Our results showed that the flagellar motors of the Halomonas strains were energized by both H+and Na+in one cell. The bimodal nature of Halomonas spp. motility with respect to the driving energy source may reflect ecophysiological versatility to adapt to a wide range of salt conditions of the marine environment.Key words: marine bacteria, Halomonas, flagellar motor, sodium, proton.

Intrinsic and extrinsic uncoupling of oxidative phosphorylation

This article reviews parameters of extrinsic uncoupling of oxidative phosphorylation (OxPhos) in mitochondria, based on induction of a proton leak across the inner membrane. The effects of classical uncouplers, fatty acids, uncoupling proteins (UCP1-UCP5) and thyroid hormones on the efficiency of OxPhos are described. Furthermore, the present knowledge on intrinsic uncoupling of cytochrome c oxidase (decrease of H(+)/e(-) stoichiometry=slip) is reviewed. Among the three proton pumps of the respiratory chain of mitochondria and bacteria, only cytochrome c oxidase is known to exhibit a slip of proton pumping. Intrinsic uncoupling was shown after chemical modification, by site-directed mutagenesis of the bacterial enzyme, at high membrane potential DeltaPsi, and in a tissue-specific manner to increase thermogenesis in heart and skeletal muscle by high ATP/ADP ratios, and in non-skeletal muscle tissues by palmitate. In addition, two mechanisms of respiratory control are described. The first occurs through the membrane potential DeltaPsi and maintains high DeltaPsi values (150-200 mV). The second occurs only in mitochondria, is suggested to keep DeltaPsi at low levels (100-150 mV) through the potential dependence of the ATP synthase and the allosteric ATP inhibition of cytochrome c oxidase at high ATP/ADP ratios, and is reversibly switched on by cAMP-dependent phosphorylation. Finally, the regulation of DeltaPsi and the production of reactive oxygen species (ROS) in mitochondria at high DeltaPsi values (150-200 mV) are discussed.

Adenine nucleotide translocase mediates the K(ATP)-channel-openers-induced proton and potassium flux to the mitochondrial matrix

KATP channel openers have been shown to protect ischemic-reperfused myocardium by mimicking ischemic preconditioning, although their mechanisms of action have not been fully clarified. In this study we investigated the influence of the adenine nucleotide translocase (ANT) inhibitors--carboxyatractyloside (CAT) and bongkrekic acid (BA)--on the diazoxide- and pinacidil-induced uncoupling of isolated rat heart mitochondria respiring on pyruvate and malate (6 + 6 mM). We found that both CAT (1.3 microM) and BA (20 microM) markedly reduced the uncoupling of mitochondrial oxidative phosphorylation induced by the K(ATP) channel openers. Thus, the uncoupling effect of diazoxide and pinacidil is evident only when ANT is not fixed by inhibitors in neither the C- nor the M-conformation. Moreover, the uncoupling effect of diazoxide and pinacidil was diminished in the presence of ADP or ATP, indicating a competition of K(ATP) channel openers with adenine nucleotides. CAT also abolished K+-dependent mitochondrial respiratory changes. Thus ANT could also be involved in the regulation of K(ATP)-channel-openers-induced K+ flux through the inner mitochondrial membrane.

Sugar retrieval by coats of developing seeds of Phaseolus vulgaris L. and Vicia faba L

Influxes of glucose, fructose and sucrose were characterised for coat cells of developing seeds of Phaseolus vulgaris L. and Vicia faba L. by monitoring uptake of [(14)C]sugars into excised seed-coat halves and two different protoplast populations derived from seed coats. Sugar influxes by the two populations of protoplasts were similar for each sugar species [sucrose > (fructose approximately glucose)] and hexoses competed with sucrose. Concentration-dependent influxes of all three sugars by excised seed coats could be described by a simple directly proportional relationship between concentration ([S]) and uptake rate (v) in the physiological range of sugar concentrations (v approximately A.[S]). Alternatively, with the exception of fructose influx by Vicia, all could be fitted to a Michaelis-Menten relationship, as could sucrose uptake by Vicia protoplasts. Apparent K(m) values were high ( approximately 100-500 mM) compared with those reported for other systems. Sucrose transport was distinct from glucose and fructose transport in both species. Sugar influx was decreased by p-chloromercuribenzenesulfonic acid, carbonylcyanide m-chlorophenylhydrazone and erythrosin B. These responses are consistent with sugar/H(+) symport acting to retrieve photoassimilates leaked to the apoplasm during post-sieve element transport within seed coats.

Functional complementation of yeast cytosolic pyrophosphatase by bacterial and plant H+-translocating pyrophosphatases

Two types of proteins that hydrolyze inorganic pyrophosphate (PPi), very different in both amino acid sequence and structure, have been characterized to date: soluble and membrane-bound proton-pumping pyrophosphatases (sPPases and H(+)-PPases, respectively). sPPases are ubiquitous proteins that hydrolyze PPi releasing heat, whereas H+-PPases, so far unidentified in animal and fungal cells, couple the energy of PPi hydrolysis to proton movement across biological membranes. The budding yeast Saccharomyces cerevisiae has two sPPases that are located in the cytosol and in the mitochondria. Previous attempts to knock out the gene coding for a cytosolic sPPase (IPP1) have been unsuccessful, thus suggesting that this protein is essential for growth. Here, we describe the generation of a conditional S. cerevisiae mutant (named YPC-1) whose functional IPP1 gene is under the control of a galactose-dependent promoter. Thus, YPC-1 cells become growth arrested in glucose but they regain the ability to grow on this carbon source when transformed with autonomous plasmids bearing diverse foreign H+-PPase genes under the control of a yeast constitutive promoter. The heterologously expressed H+-PPases are distributed among different yeast membranes, including the plasma membrane, functional complementation by these integral membrane proteins being consistently sensitive to external pH. These results demonstrate that hydrolysis of cytosolic PPi is essential for yeast growth and that this function is not substantially affected by the intrinsic characteristics of the PPase protein that accomplishes it. Moreover, this is, to our knowledge, the first direct evidence that H+-PPases can mediate net hydrolysis of PPi in vivo. YPC-1 mutant strain constitutes a convenient expression system to perform studies aimed at the elucidation of the structure-function relationships of this type of proton pumps.

Lansoprazole for maintenance of remission of erosive oesophagitis

Gastro-oesophageal reflux disease, which is experienced daily by a significant proportion of individuals, may result in serious sequelae such as erosive oesophagitis. Short-term treatment with acid antisecretory therapy (a proton pump inhibitor or a histamine H(2) receptor antagonist) is highly effective in healing the erosive oesophagitis lesion. However, numerous studies confirm that unless maintenance therapy is initiated virtually all patients will experience oesophagitis relapse within 1 year, as well as an increasing severity of oesophagitis and risk for complications such as Barrett's oesophagus and adenocarcinoma. Studies evaluating the efficacy of proton pump inhibitor and H(2) antagonist maintenance therapy have found that only the proton pump inhibitors significantly reduce the incidence of oesophagitis relapse. Pharmacoeconomic studies have also confirmed that proton pump inhibitor maintenance therapy is cost effective, by virtue of the ability of these agents to reduce the incidence of relapse as well as prolong the time to relapse and increase the number of weeks per year that patients are without symptoms. Lansoprazole, a member of the proton pump inhibitor class of agents, has been extensively studied in the treatment of patients with a variety of acid-related disorders. Among those with erosive oesophagitis, maintenance therapy with lansoprazole 15 or 30mg once daily is highly effective in preventing relapse. Studies have documented that lansoprazole 15 and 30mg once daily for six months prevents oesophagitis relapse in up to 81 and 93% of patients, respectively, with comparable percentages of patients remaining in remission after 1 year of treatment. These high rates of remission have also been observed in studies of patients with lesions that were difficult to heal at baseline (resistant to healing with at least 3 months of H(2) antagonist therapy). Moreover, lansoprazole produces high remission rates regardless of the grade of erosive oesophagitis before acute healing. Among symptomatic patients with heartburn, lansoprazole provides rapid and effective relief of daytime and night-time heartburn and prevents relapse of symptoms. Lansoprazole has a wide margin of safety and is well tolerated when administered as monotherapy in short- and long-term clinical trials. Taken together these data suggest that proton pump inhibitor therapy represents the preferred and ideal long-term management strategy for the patient with erosive oesophagitis. Lansoprazole is a well-established member of this class of agents and, as such, has an extensive body of literature that supports its safety, tolerability and clinical efficacy in preventing relapse in these patients.

Action of palytoxin on apical H+/K+-ATPase in rat colon

Palytoxin stimulated a cation-dependent short-circuit current (Isc) in rat distal and proximal colon in a concentration-dependent fashion when applied to the mucosal surface of the tissue. The distal colon exhibited a higher sensitivity to the toxin. The palytoxin-induced Isc was blocked by vanadate but was resistant to ouabain or scilliroside, suggesting the conversion of a vanadate-sensitive H+/K+-ATPase into an electrogenic cation transporter. Cation substitution experiments with basolaterally depolarized tissues suggested an apparent permeability of the palytoxin-induced conductance of Na+>K+>Li+. Immunohistochemical control experiments confirmed the absence of the Na+/K+-ATPase in the apical membrane. Consequently, the pore-forming action of palytoxin is not restricted to Na+/K+-ATPase but is also observed with the colonic H+/K+-ATPase.

V-type H+-ATPase in the human eccrine sweat duct: immunolocalization and functional demonstration

We investigated for the presence of a vacuolar-type H+-ATPase (V-ATPase) in the human eccrine sweat duct (SD). With the use of immunocytochemistry, an anti-V- ATPase antibody showed a strong staining at the apical membrane and a weaker one in the cytoplasm. Cold preservation followed by rewarming did not alter this staining pattern. With the use of the pH-sensitive dye 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein on isolated and perfused straight SD under HCO-free conditions and in the absence of Na+, proton extrusion was determined from the recovery rate of intracellular pH (dpH(i)/dt) following an acid load. Oligomycin (25 microM), an inhibitor of F-type ATPases, decreased dpH(i)/dt by 88 +/- 6%, suggesting a role for an ATP-dependent process involved in pH(i) recovery. Moreover, dpH(i)/dt was inhibited at 95 +/- 3% by 100 nM luminal concanamycin A, a specific inhibitor of V-ATPases, whereas 10 microM bafilomycin A1, another specific inhibitor of V-ATPases, was required to decrease dpH(i)/dt by 73%. These results strongly suggest that a V-ATPase is involved in proton secretion in the human eccrine SD.

Targets of anti-influenza chemotherapy other than neuraminidase and proton pump

Antiviral chemotherapy for influenza started with treatment with amantadine and then progressed with finding the clinical efficacy of neuraminidase (NA) inhibitors. Beside amantadine and NA inhibitors, there are several compounds that attack novel targets of influenza virus (FluV) replication. Binding and penetration of FluV to cell membrane are important stages in the process of virus replication, and several compounds that inhibit these functions have been reported, although most of them have yet to be examined for clinical use. A polyoxometalate (PM523) was shown to be potent inhibitor of FluV A, respiratory syncytial virus and measles virus, and was shown to inhibit membrane fusion between FluV envelope and the cellular membrane. Strains of virus with acquired resistance to PM523 had mutations in the amino acids substrates in HA1 head, and amino acid changes occurred in the interface peptide of the trimers of HA. Cap formation of FluV-encoded mRNA is unique; it utilizes 5'-mGpppXm of host mRNA. Several substances which inhibit the cap formation of FluV (they are inhibitors of PB2 enzyme activity of FluV) are introduced and reviewed in this article. A metabolic product of ribavirn, 1,2,4 triazole carboxamide (T-CONH2) is inhibitory for FluV A growth in vitro. Peroral administration of TCONH2 also showed therapeutic effect in an experimental mouse infection model of FluV A as well as ribavirin. TCONH2 seems to be less toxic than ribavirin for mice, and may be useful as alternative chemotherapy of ribavirin. Other anti-FluV substances that have been reported to be effective for FluV infection in the mouse are discussed with respect to the possibility of their clinical potential.

Potassium drives daily reversible thallus enlargement in the marine red alga Porphyra leucosticta (Rhodophyta)

Growth rate in terms of area expansion per 30 min was measured in the marine red algae Porphyra leucosticta under light/dark cycles of 6:6 h. Thalli grown in artificial seawater (ASW), under controlled ionic concentrations, showed a rapid thallus expansion just after light-on (morning-peak). Dark phase began with a significant thallus contraction (dark-peak) but no growth was observed until the next light phase. The removal of K+ from the medium inhibited the reversible growth peak that this species shows after light-on. On the other hand, the removal of Na+ did not have an apparent effect on growth pattern. Addition of Rb+ to K+-free ASW restored the morning-peak to 60% of its value in ASW, but addition of Li+ failed to restore the morning-peak. Intracellular ion analyses revealed that after light-on, the internal K+ content of the cells of this species increased 4-fold in 90 min, reaching an intracellular concentration of up to 300 micromol K+ per gram fresh weight, and that this value remained fairly constant over the light phase. Addition of 100 mM of tetraethylammonium, a specific K+-channel blocker, inhibited the morning-peak by 40%. The Na+ and Cl- contents in the cells increased rapidly in the first 45 min of the light phase, but then the internal concentrations of both ions decreased to their minimum values in the light phase. The carbonic anhydrase inhibitors acetazolamide and 6-ethoxyzolamide did not affect thallus expansion during the light phase. In contrast, thallus expansion in the light phase was completely inhibited by diethylstilbestrol, an inhibitor of the putative primary pump, and by 3-(3',4'-dichlorophenyl)-1,1-dimethylurea (DCMU), an inhibitor of photosynthesis, but not by sodium vanadate, a specific inhibitor of the plasma-membrane H+-ATPase. We suggest that the periodic oscillation of the short-term growth rate of P. leucosticta occurs in response to potassium fluxes, which control the osmotic pressure and eventually the relative cell volume. The possible effects of the loosening of the cell wall and the internal K+ concentration on the growth of this species are also discussed.

[Pharma-clinics medication of the month. Rabeprazole (Pariet)]

Proton pomp inhibitors (PPI) have revolutionized the treatment of gastro-oesophageal reflux disease and gastro-duodenal ulcers. Rabeprazole (Pariet) is the last PPI arrived on the Belgian market. Controlled studies have shown an efficacy similar to emeprazole in the treatment of oeso-gastro-duodenal acid diseases. Rabeprazole has a favourable profile with rapid action and good safety.

Should anti-Helicobacter therapy be different in patients with dyspepsia compared with patients with peptic ulcer diathesis?

Physicians should try to reach an optimal cure rate with initial anti-Helicobacter therapy. Helicobacter pylori infection in patients with peptic ulcer disease (PUD) is more likely to be cured then in patients with 'functional' dyspepsia (FD). Differences in cure rates of 5-15% are usually reported, which is considered to be clinically relevant. Different strains (virulent v. non-virulent) in PUD and FD may induce different alterations in the gastric mucosa, and thereby either facilitate or impair antimicrobial efficacy. A study in this journal showed that triple therapy with ranitidine bismuth citrate (RBC) was superior to triple therapy with a proton pump inhibitor (PPI), but only in the more-difficult-to-cure FD patients. Clinicians should be aware that most published treatment studies have included only PUD patients. This means that in clinical practice the cure rates obtained in patients with FD or even uninvestigated dyspepsia will usually be lower then those reported in the literature. One way to deal with this is to consider prolonging the duration of an initial anti-Helicobacter therapy from 7 to 10 or 14 days in patients without ulcers.

In situ analysis of pH gradients in mosquito larvae using non-invasive, self-referencing, pH-sensitive microelectrodes

The alkaline environment, pH approximately 11, in the anterior midgut lumen of mosquito larvae is essential for normal nutrition and development. The mechanism of alkalization is, however, unknown. Although evidence from immunohistochemistry, electron microscopy and electrophysiology suggests that a V-ATPase is present in the basal membranes of the epithelial cells, its physiological role in the alkalization process has not been demonstrated. To investigate a possible role of the V-ATPase in lumen alkalization, pH gradients emanating from the hemolymph side of the midgut in semi-intact mosquito larvae were measured using non-invasive, self-referencing, ion-selective microelectrodes (SERIS). Large H+ concentration gradients, with highest concentrations close to the basal membrane (outward [H+] gradients), were found in the anterior midgut, whereas much smaller gradients, with concentrations lowest close to this membrane (inward [H+] gradients), were found in the gastric caeca and posterior midgut. Similar region-specific pH gradients, with consistent anterior-to-posterior profiles, were observed in individuals of two Aedes species, Aedes aegypti from semi-tropical Florida and Aedes canadensis from north-temperate Massachusetts. The gradients remained in a steady state for up to 6 h, the maximum duration of the recordings. Bafilomycin A1 (10(−5), 10(−7)mol × l(−1)) on the hemolymph side greatly diminished the [H+] gradients in the anterior midgut but had no effect on the gradients in the gastric caecum and posterior midgut. These physiological data are consistent with the previous findings noted above. Together, they support the hypothesis that a basal, electrogenic H+ V-ATPase energizes luminal alkalization in the anterior midgut of larval mosquitoes.

The proton uptake channel of bacteriorhodopsin as studied by a photoelectrochemical method

A series of the mutant proteins (D96N, D96N/D85N, D115N, L93T, T46V, V49A) where the residues are located at the cytoplasmic domain of bacteriorhodopsin (bR) were studied photoelectrochemically and their photocurrent response characteristics at the electrode/electrolyte interface were compared with those of the wild-type bR. While the wild-type bR of normal proton pumping activity yields symmetrical cathodic (positive) and anodic (negative) responses, corresponding to proton release and proton uptake, respectively, these mutants, with the exception of D115N, showed diminished amplitudes in the negative response. This indicates retardation of proton translocation from the cytoplasmic surface to the retinal Schiff base. The mutation that gave the strongest influence on the negative response was D96N while moderate influence was obtained with L93T, T46V, and V49A. These results suggest that residues other than D96 also participate in the cytoplasmic proton uptake channel, either by interacting with D96 directly or by forming a hydrogen-bonded network with water molecules. The D96N/D85N double mutant yielded little response at neutral pH, but the response was partially recovered by addition of azide, while it was fully recovered in the single mutant D96N. The D115N mutant showed the response profile that closely resembles the wild-type, indicating that D115 is not crucially involved in the event of proton transfer relay at the cytoplasmic region. It was also found that every mutant in this study releases protons prior to uptake at the other membrane surface, as does the wild-type.

A flowcytometric method for evaluation of acid secretion from isolated rat gastric mucosal cells

Studies on the gastric proton pump are mostly performed on the H(+), K(+)-ATPase enzyme in the microsomal preparation or by aminopyrine accumulation in the gastric parietal cells. H(+), K(+)-ATPase activity is estimated by both spectrophotometric and fluorimetric methods. In the present study, quenching or augmentation in acridine orange (AO) fluorescence was monitored on a flowcytometer in rat gastric mucosal cells. Rat gastric mucosal cells were isolated by the standard pronase--EDTA method. The effect of oleic acid, a proton pump inhibitory was evaluated on gastric parietal cell activity and was compared with its effect on proton transport, H(+), K(+)-ATPase, and p-nitrophenyl phosphatase (p-NPPase) activity in gastric microsomes. In addition, the effect of histamine and carbachol, gastric acid release inducers, was also investigated by flowcytometry in isolated parietal cells. Histamine and carbachol, in a dose-dependent manner, stimulated acid release from isolated gastric cells. Oleic acid also dose-dependently inhibited the basal and stimulated acid release from the cells, as well as in all three enzyme preparations associated with gastric proton pump activity. Thus, the results suggest that flowcytometric method might be used to study basal, as well as stimulated, proton pump activity in isolated gastric parietal cells.

Total acid suppression and its effect on Barrett's esophagus

Barrett's esophagus is a complication of gastroesophageal reflux disease (GERD) and may result from prolonged acid exposure in the esophagus. As a result, clinicians are investigating a possible relationship between acid suppression and a decrease in the risk of Barrett's esophagus progression. Some studies suggest that the length of Barrett's esophagus may be reduced with total acid suppression therapy. Other studies indicate that patients with Barrett's esophagus are less sensitive to acid-induced symptoms (e.g., heartburn). While these patients may feel better symptomatically, the acid may not be sufficiently reduced to prohibit further damage. Acid suppression, even on high-dose pharmacotherapy, does not always eliminate the nocturnal acid breakthroughs. The contrasting study results on this issue are discussed.

Managed care issues in the treatment of gastroesophageal reflux disease

The impact that reflux disease has on patients' quality of life is reviewed and some of the managed care issues surrounding treatment, including the step-up/step-down philosophy and a comparison of available proton pump inhibitor (PPI) agents, are explored. PPIs are first-line pharmacotherapy for treating reflux disease. They have shown superior efficacy compared with previously recommended agents. Whereas PPI therapy has some limitations, it offers substantial benefits in terms of clinical and quality-of-life factors.

[Treatment of Helicobacter pylori infection]

The recommended treatment of Helicobacter pylori infection is a seven-day course of the following regimen: a double dose proton-pump inhibitor (omeprazole 2 x 20 mg, or lansoprazole 2 x 30 mg, or pantoprazole 2 x 40 mg), associated with 2 antibiotics (amoxicillin 2 x 1,000 mg, clarithromycin 2 x 500 mg). Eradication rate is around 65%. Main causes of failure are antibiotic resistance, bad compliance, early termination of therapy due to adverse events. A second line treatment is possible with substitution of clarithromycine by metronidazole (3 x 500 mg), a longer duration of treatment (14 days) and sometimes a quadritherapy with bismuth (not available in France).

Role of drug therapy in the treatment of gastro-oesophageal reflux disorder in children

Gastro-oesophageal reflux (GOR) is the effortless passage of gastric contents into the distal oesophagus. It can be classified as functional (or symptomatic), in which the infant remains free from disease, or a pathological (GOR disease, GORD), in which gastrointestinal, respiratory or neurobehavioural signs occur with intraoesophageal acidification and the development of oesophagitis. Functional or symptomatic GOR is successfully treated by conservative measures and does not require investigative diagnostic tools; however, both drug administration and an investigative approach are mandatory in patients with GORD. There is currently a great range of proven therapeutic options for GORD that are directed at counteracting the pathogenetic components of the disorder. In this report we discuss the role of different drug classes for treating GORD in children. The choice of therapy for GORD depends upon the severity of signs and the degree of oesophagitis. The presence of oesophagitis, as documented by endoscopy, suggests the use of antisecretory drugs; H2 receptor antagonists are the first-line agents. Nevertheless, individuals with refractory disease or those patients requiring potent inhibition of acid secretion (for example, GORD with respiratory involvement) can be given proton pump inhibitors. Other groups of patients who need potent inhibition of acid secretion are children with neurological dysfunction and those with Barrett's oesophagus. It is still unclear whether patients with frequent relapses are candidates for long term administration of antisecretory drugs or for surgical fundoplication.

Characterization of cardioprotection mediated by AT2 receptor antagonism after ischemia-reperfusion in isolated working rat hearts

BACKGROUND

Whether cardioprotection induced by the angiotensin II (AngII) type 2 receptor (AT(2)R) antagonist PD123,319 (PD) after ischemia-reperfusion (IR) is influenced by the concentration of PD, presence of AngII, timing of exposure, or inhibition of proton production from glucose metabolism is not known.

METHODS AND RESULTS

We examined these factors in isolated working rat hearts subjected to IR injury, no treatment (control), or treatment with N(6)-cyclohexyl adenosine (CHA, 0.5 micromol/L), an adenosine A(1) receptor agonist that induces cardioprotection by decreasing protons ("positive" control). Compared with control, 1 micromol/L PD present throughout IR improved recovery of left ventricular work (73 +/- 5 vs. 40 +/- 8%) to the level with CHA (82 +/- 5%), but 0.1 micromol/L PD did not (58 +/- 6 vs. 40 +/- 8%). AngII (1 nmol/L) did not effect postischemic recovery associated with 1 micromol/L PD (73 +/- 7%) but improved that associated with 0.1 micromol/L PD (86 +/- 3%). PD (1 micromol/L), present solely during reperfusion, enhanced postischemic left ventricular recovery to 72 +/- 5%. Also, PD (1 micromol/L) did not affect glycolytic rates or proton production in nonischemic or IR hearts.

CONCLUSION

PD-induced cardioprotection is 1) PD concentration-dependent, 2) AngII-sensitive, 3) mediated during reperfusion, and 4) independent of proton production, suggesting that reduction in IR injury and indirect AT(1)R stimulation might be involved.

Ion currents involved in early Nod factor response in Medicago sativa root hairs: a discontinuous single-electrode voltage-clamp study

Nod factor [NodRm-IV(Ac,S)], isolated from the bacterium Rhizobium meliloti, induces a well-known depolarization in Medicago sativa (cv Sitel) root hairs. Analysis of this membrane response using the discontinuous single-electrode voltage-clamp technique (dSEVC) shows that anion channel, K+ channel and H+-ATPase pump currents are involved in young growing root hairs. The early Nod-factor-induced depolarization is due to increase of the inward ion current and inhibition of the H+ pump. It involved an instantaneous inward anion current (IIAC) and/or a time-dependent inward K+ current (IRKC). These two ion currents are then down-regulated while the H+ pump is stimulated, allowing long-term rectification of the membrane potential (Em). Our results support the idea that the regulation of inward current plays a primary role in the Nod-factor-induced electrical response, the nature of the ions carried by these currents depending on the activated anion and/or K+ channels at the plasma membrane.