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Biomedical subjects

A Ghazi

Publications and source records attributed to A Ghazi.

At least 19 recordsLinked to original sources
PubMed1993

Insect defensin, an inducible antibacterial peptide, forms voltage-dependent channels in Micrococcus luteus.

Insect defensins are cationic, cysteine-rich peptides (approximately 4 kDa) that appear after bacterial challenge or injury in the hemolymph of insects belonging to a large variety of orders. These peptides possess anti-Gram-positive activity and participate in the potent antibacterial defense reactions of insects. Using recombinant insect defensin and the strain Micrococcus luteus as a test organism, we have investigated the mode of action of this peptide. We show that defensin disrupts the permeability barrier of the cytoplasmic membrane of M. luteus, resulting in a loss of cytoplasmic potassium, a partial depolarization of the inner membrane, a decrease in cytoplasmic ATP, and an inhibition of respiration. Potassium loss is inhibited below the order-disorder transition of the lipid hydrocarbon chains. It is also inhibited by divalent cations and by a decrease in the membrane potential below a threshold of 110 mV. We propose that these permeability changes reflect the formation of channels in the cytoplasmic membrane by defensin oligomers. This proposal is supported by patch-clamp experiments that show that insect defensins form channels in giant liposomes.

Adenosine Triphosphate↗
PubMed1993

Voltage-dependent cationic channel of Escherichia coli.

A fraction highly enriched with inner membranes of E. coli was fused with liposomes, using the dehydration-rehydration technique, to produce giant liposomes amenable to patch-clamp recordings. Among the several channels present in this type of preparation, one was further characterized. The channel has a conductance of some 200 pS (in 0.1 M KCl) and is weakly selective for cations (PK/PCl = 4). The channel stays open at negative and low positive membrane potentials and shows an increasing probability of closure with increasing voltage. High positive membrane potentials favor transitions to a long-lived inactivated state, following slow kinetics. Voltage-dependent rapid flickerings of the same amplitude, between open state and other short-lived closed states, are superposed on these kinetics. The channel is presumed to be localized in the inner membrane, but its characteristics are also compatible with those of porins of the outer membrane. However, the major porins OmpF and OmpC, purified and reconstituted into giant liposomes, exhibited a marked different behavior.

Bacterial Outer Membrane Proteins↗
PubMed1993

Impairment of neuromotor and cognitive development in iodine-deficient schoolchildren with normal physical growth.

In order to detect somatic and psychomotor disturbances in children and adolescents residing in areas of iodine deficiency, schoolchildren from three areas with different degrees of iodine deficiency were studied. In Randan, the prevalence of severe endemic goiter was accompanied by alteration in thyroid function, increased thyrotropin levels and retardation of both bone and psychomotor age and decreased intellectual quotient. In Tehran, where iodine deficiency is mild, visible goiter was present in 15% of schoolchildren but no alterations in thyroid function, serum thyrotropin, somatic or psychomotor development could be detected. In Zagoon, where the prevalence and severity of goiter was less than Randan but more than Tehran, thyroid function was normal but slightly decreased as compared to Tehran; somatic development was unaltered, but retardation in psychomotor development was evident and the mean intellectual quotient was less than that of Tehranian schoolchildren. These findings indicate the occurrence of physical and psychomotor disturbances in apparently normal schoolchildren from areas of iodine deficiency. Alteration in psychomotor development may occur in children with normal physical growth, due to iodine deficiency.

Adolescent↗
PubMed1992

Fast and slow kinetics of porin channels from Escherichia coli reconstituted into giant liposomes and studied by patch-clamp.

E. coli porins (OmpF and OmpC) were purified and reconstituted into liposomes which were enlarged to giant proteoliposomes by dehydration-rehydration and studied by patch-clamp. The porins could be closed by voltage pulses under -100 mV. The kinetics of closure was slow, with closure events of about 200 pS in 0.1 M KCl. Rapid fluctuations (in the millisecond range) of about one third (60-70 pS) of the large closure steps were also observed. The data are interpreted as follows: an increase in membrane potential favours the cooperation transition of multimers towards an inactivated state, while monomers which have not been inactivated can flicker rapidly between an open and a short-lived closed state.

Bacterial Outer Membrane Proteins↗
PubMed1992

Gadolinium ion inhibits loss of metabolites induced by osmotic shock and large stretch-activated channels in bacteria.

Bacteria subjected to a hypotonic osmotic shock lose internal ions and also metabolites, without lysis of the cells. We show that the presence in the shock medium, at submillimolar concentrations, of the ion gadolinium, recently shown to block stretch-activated channels in Xenopus oocytes [Yang, X.-C. & Sachs, F. (1989) Science 243, 1068-1071], was sufficient to inhibit shock-induced release of metabolites such as lactose and ATP in Escherichia coli and ATP in Streptococcus faecalis. Moreover, gadolinium was observed, in patch-clamp experiments, to inhibit the giant stretch-activated channels of E. coli, S. faecalis. and Bacillus subtilis. Taken together, these data suggest that stretch-activated channels are localized in the cytoplasmic membrane of Gram-negative and Gram-positive bacteria, where they control the efflux of osmotic solutes, thus probably playing a major role in the response to hypotonic osmotic shock.

Adenosine Triphosphate↗
PubMed1992

Excretion of glutamate from Corynebacterium glutamicum triggered by amine surfactants.

Corynebacterium glutamicum is used for the industrial production of glutamate. Excretion of the amino acid may be induced by various means. We have analyzed the characteristics of glutamate excretion induced by two amine surfactants, dodecylammonium acetate (DA) and dodecyltrimethylammonium bromide (DTA). Addition of these surfactants induced an immediate efflux of internal glutamate. It also induced a perturbation of the energetic parameters of the cell (decrease of delta mu H, decrease of the internal ATP concentration). The efflux was not the result of these perturbations: glutamate is taken up by the cells via an ATP-dependent unidirectional active transport system and no efflux took place as a consequence of an artificial decrease of the energetic parameters. In addition, amine surfactants also induced an excretion of other species, in particular potassium. We have tested the possibility that the effluxes result from a permeabilization of the lipid bilayer by analyzing the interactions between the surfactants and liposomes.

Adenosine Triphosphate↗
PubMed1992

Endoscopic papillotomy while the gallbladder is in situ.

The authors report on their experience with 25 patients who underwent an endoscopic papillotomy with gallbladder in situ and review the current literature on this topic. Twenty-four out of 25 patients in this study had their common bile duct cleared of stones. Five patients (24%) required cholecystectomy on follow-up at an average of 14.4 months. There was no mortality associated with the procedure. The authors' experience and review of the literature suggest that endoscopic papillotomy plays an important role in the removal of common bile duct stones in persons who have their gallbladder in situ, especially in those patients who are at high risk for surgery, either because of advanced age or other medical problems. However, the use of endoscopic papillotomy alone in young, healthy persons is more problematic because of the relatively high rate of cholecystitis or recurrent biliary colic necessitating a cholecystectomy at a later date. The authors suggest that, in the future, the ideal treatment regimen for common bile duct stones in patients with their gallbladder in situ may be urgent endoscopic papillotomy with a scheduled elective laparoscopic cholecystectomy.

Adult↗
PubMed1991

Effect of osmotic pressure on membrane energy-linked functions in Escherichia coli.

Osmotic upshock of E. coli cells in NaCl or sucrose medium resulted in a large decrease in the cytoplasmic volume and the inhibition of growth, of the electron transfer chain and of four different types of sugar transport system: the lactose proton symport, the glucose phosphotransferase system, the binding-protein dependent maltose transport system and the glycerol facilitator. In contrast to NaCl and sucrose, the permeant solute glycerol had no marked effect. These inhibitions could be partially relieved by glycine betaine. Despite these inhibitions, the internal pH, the protonmotive force and the ATP pool were maintained. It is concluded that inhibition of electron transfer and of sugar transport is the consequence of conformational changes caused by the deformation of the membrane. It is also concluded that the arrest of growth observed upon osmotic upshock is not due to energy limitations and that it cannot be explained by the inhibition of carbohydrate transport.

Adenosine Triphosphate↗
PubMed1989

A patch-clamp study of ion channels of inner and outer membranes and of contact zones of E. coli, fused into giant liposomes. Pressure-activated channels are localized in the inner membrane.

Inner and outer membranes of Escherichia coli and contact zones were isolated and fused separately with giant liposomes amenable to patch-clamp recording. Different types of large pressure-activated channels were localized in the inner membrane fraction which also contained smaller, pressure-insensitive channels. The outer membrane contained pressure-insensitive channels with large conductances and long opening and closing times which are likely to be porins. Large channels were also observed in contact zones.

Cell Fractionation↗
PubMed1989

Endoscopic retrograde cholangiopancreatography, endoscopic sphincterotomy, and biliary drainage.

Endoscopic retrograde cholangiopancreatography, endoscopic sphincterotomy, and endoscopic biliary drainage have dramatically changed the diagnosis and management of disorders of the pancreas and hepatobiliary tract. Endoscopic retrograde cholangiopancreatography will provide a high-resolution study that will define accurately the nature and location of the disease process involving the pancreas or bile ducts. Although sonography, CT, and, recently, MRI may provide clues to the diagnosis, it often remains for endoscopic retrograde cholangiopancreatography to establish the diagnosis with certainty. Endoscopic sphincterotomy has been invaluable in the management of common bile-duct stones. In patients who have had their gallbladders removed, sphincterotomy has avoided reoperation in the same field and the risk of general anesthesia. Sphincterotomy also is assuming an increasingly important role in the management of common-duct stones in patients with their gallbladders in situ who are poor operative candidates. In these patients, sphincterotomy likewise avoids the risk of general anesthesia and the surgical stress of opening a major body cavity. The technique has also proved to be helpful in the palliative treatment of ampullary and distal common bile-duct carcinomas in those patients who are poor operative candidates. Finally, sphincterotomy has found a role in the treatment of choledochal cysts and may provide relief of pain in those patients with the elusive diagnoses of postcholecystectomy syndromes, biliary dyskinesias, and sphincter of Oddi dysfunction. Endoscopic biliary drainage is becoming an increasingly popular option for the palliation of malignant biliary obstruction. In those patients who are poor operative candidates, the risk of general anesthesia and major surgery is avoided. In those patients with obviously incurable tumors, endoscopic drainage allows for a brief hospitalization without surgery in the face of a short life expectancy.

Adult↗
PubMed1989

Calibration curves for size-exclusion chromatography: description of HPLC gels in terms of porous fractals.

We have tested the proposition that porous media used in protein size exclusion chromatography are surface fractals. The data obtained in the calibration of classical gels (Sephacryl and Sepharose) and of HPLC gels (TSK SW and PW) using a wide range of protein sizes, have been analyzed within the framework of this theory. While the model does not apply to classical gels, it seems that HPLC gels can be described as fractals in the range of protein sizes. This finding has interesting implications for the calibration procedure.

Calibration↗
PubMed1988

Impact on energy metabolism of quantitative and functional cyclosporine-induced damage of kidney mitochondria.

In this study we have measured, under experimental conditions which maintained efficient coupling, respiratory intensity, respiratory control, oxidative phosphorylation capacity and protonmotive force. Succinate cytochrome-c reductase and cytochrome-c oxidase activities were also studied. These investigations were carried out using kidney mitochondria from cyclosporine-treated rats (in vivo studies) and from untreated rats in the presence of cyclosporine (in vitro studies). Inhibition of respiratory intensity by cyclosporine did not exceed 21.1% in vitro and 15.9% in vivo. Since there was no in vitro inhibition of succinate cytochrome-c reductase and cytochrome-c oxidase activities, the slowing of electron flow observed can be interpreted as a consequence of an effect produced by cyclosporine between cytochromes b and c1. Cyclosporine had no effect on respiratory control either in vitro or in vivo. Statistically significant inhibition of the oxidative phosphorylation was observed both in vitro (6.6%) and in vivo (12.1%). Moreover, cyclosporine did not induce any change of membrane potential either in vivo or in vitro. Our findings show that cyclosporine is neither a protonophore, nor a potassium ionophore. In cyclosporine-treated rats we notices a decrease of protein in subcellular fraction, including the mitochondrial fraction. The role of the inhibition respiratory characteristics by cyclosporine in nephrotoxicity in vivo must take account of these two parameters: inhibition of the respiratory characteristics measured in vitro and diminution of mitochondrial protein in cyclosporine-treated rats.

Animals↗
PubMed1987

The use of gel chromatography for the determination of sizes and relative molecular masses of proteins. Interpretation of calibration curves in terms of gel-pore-size distribution.

The separation of proteins by gel-exclusion chromatography has been explained in terms of partitioning of the macromolecules within the gel by a distribution of pores of various radii. The assumption that the distribution of pore sizes is Gaussian has led to the prediction of a linear relationship between the molecular Stokes radius (RS) of the protein and the function erf-1 (1-KD), where KD is the partition coefficient [Ackers (1967) J. Biol. Chem. 242, 3237-3238]. Since careful calibrations of classical (agarose and dextran) gels and h.p.l.c. gels have shown that such a linear relationship is not verified experimentally over a wide range of native protein sizes, we have reinvestigated the model of Ackers (above reference). We show that Ackers' (above reference) derivation is not valid except for a particular Gaussian distribution of pore sizes centred at the origin. Relaxation of this restriction to allow for other types of Gaussian distributions cannot account for the non-linear calibration curves that we have obtained. Instead we show that the pore-size distribution can be calculated from the experimentally determined function KD = f(RS) and that this distribution is bimodal (non-Gaussian). One distribution is centred below 2 nm, whereas the mean value of the second one is around 6-8 nm. The minimum in this bimodal distribution corresponds, for some gels, to a region of poor resolution, which needs to be appreciated for the proper use of gel chromatography in the determination of molecular size.

Chromatography, Gel↗
PubMed1987

Endoscopic management of choledochocele. A case report and review of the English literature.

Choledochocele or type III choledochal cyst is a rare lesion of the biliary tree. It may be of acquired or congenital etiology and can assume one of two anatomic variants. Either the common bile duct and the pancreatic duct enter the choledochocele together, or it is formed by the common bile duct alone with the pancreatic duct entering as a separate opening. The most frequent presenting symptoms are abdominal pain, pancreatitis, and jaundice. Traditional therapy has been either marsupialization of the cyst into the duodenum or complete surgical excision. This paper cites the eighth patient reported in the English-language literature whose choledochocele was treated endoscopically. It is the authors' opinion that either an endoscopic papillotomy or an endoscopic fistulotomy with extension of the incision over the cyst is the simpler and preferred method of treatment.

Aged↗
PubMed1986

Absence of a unique relationship between active transport of lactose and protonmotive force in E. coli.

The relationship between active transport of lactose via the lactose permease and the protonmotive force has been determined in E. coli cells using either the respiratory chain inhibitor cyanide or protonophores to decrease the protonmotive force progressively. In contradiction with the prediction of the delocalized chemiosmotic theory, two different relationships were obtained depending on the method used.

Biological Transport, Active↗