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Biomedical subjects

A Walter

Publications and source records attributed to A Walter.

At least 127 records · Page 7Linked to original sources
PubMed1983

Escherichia coli outer membrane protein K is a porin.

Protein K is an outer membrane protein found in pathogenic encapsulated strains of Escherichia coli. We present evidence here that protein K is structurally and functionally related to the E. coli K-12 porin proteins (OmpF, OmpC, and PhoE). Protein K was found to cross-react with antibody to OmpF protein and to share 8 out of 17 peptides in common with the OmpF protein. Strains that are OmpC porin- and OmpF porin- and contain protein K as their major outer membrane protein have increased rates of uptake of nutrients and a faster growth rate relative to the parental porin- strain. The protein K-containing strains are at least 1,000-fold more sensitive to colicins E2 and E3 than is the porin -deficient strain. These data suggest that protein K is a functional porin in E. coli. The porin function of protein K was also demonstrated in vitro, using black lipid membranes. Protein K increased the conductance in these membranes in discrete, uniform steps characteristic of channels with a size of about 2 nS.

Bacterial Outer Membrane Proteins↗
PubMed1982

SCN-and HSCN transport through lipid bilayer membranes. A model for SCN- inhibition of gastric acid secretion.

Diffusion of thiocyanate (SCN-) and thiocyanic acid (HSCN) (pK=-1.8) through lipid bilayer membranes was studied as a function of pH. Membranes were made of egg phosphatidylcholine or phosphatidylcholine plus cholesterol (1:1 mol ratio) dissolved in decane or tetradecane. Tracer fluxes and electrical conductances were used to estimate the permeabilities to HSCN and SCN-. Over the pH range 1.0 to 3.3 only HSCN crosses the membrane at a significant rate. The relation between the total SCN flux (JA), concentrations and permeabilities is: 1/JA = 1/pul([A-]+[HA])+1/pm HA[HA], where [a-] and [HA] are the concentrations of SCN- and HSCN, pul is permeability coefficient of the unstirred layer, and PmHA is the membrane permeability to HSCN. By fitting this equation to the data we find that PmHA = 2.6 cm.s-1 and Pul = 9.0.10-4 cm .s-1. Conductance measurements indicate that PmA- is 5.10-9 cm.s-1. Addition of cholesterol to phosphatidylcholine (1:1 mol ratio) reduces PmHA by a factor of 0.4 but has no effect on PmA-. SCN- is potent inhibitor of acid secretion in gastric mucosa, but the mechanism of SCN- action is unknown. Our results suggest that SCN- acts by combining with H+ in the mucosal unstirred layer (secretory pits) and diffusing back into the cells as HSCN, thus dissipating the proton gradient across the secretory membrane. A similar mechanism of cation is proposed for some other inhibitors of gastric acid secretion, e.g. nitrite (NO2-), cyanate (CNO-) and NH4+.

Animals↗
PubMed1982

Weak acid permeability through lipid bilayer membranes. Role of chemical reactions in the unstirred layer.

The premeabilities of planar lipid bilayer (egg phosphatidylcholine-decane) membranes to butyric and formic acids were measured by tracer and pH electrode techniques. The purposes of the study were (a) to establish criteria for the applicability of each method and (b) to resolve a discrepancy between previously published permeabilities determined using the different techniques. Tracer fluxes of butyric acid were measured at several concentrations and pH's. Under symmetrical conditions the one-way flux of butyric acid(J) is described by 1/J = 1/Pul ([HA] + [A-]) + 1/Pm([HA]), where Pul and Pm are the unstirred layer and membrane permeability coefficients. Pm determined in this manner is 950 x 10(4) cm s-1. Published values for the butyric acid permeability for egg phosphatidylcholine-decane bilayers are 11.5 x 10(-4) (Wolosin and Ginsburg, 1975) and 640 x 10(-4) cm s-1 (Orbach and Finkelstein, 1980). Wolosin and Ginsburg measured net fluxes from a solution of pH = Pka into an unbuffered solution containing a pH electrode. Orbach and Finkelstein measured tracers fluxes under symmetrical conditions at pH 7.4. We reproduced the results of Wolosin and Ginsburg and showed that their apparently low Pm was caused by unstirred layer effects in their poorly buffered solutions. The permeability to formic acid (pKa = 3.75) measured by both tracer and pH electrode techniques was approximately 10(-2) cm s-1. However, if pm greater than Pul, the pH electrode technique cannot be used for measuring the permeabilities of weak acids with pKa's greater than approximately 4.

Alkanes↗
PubMed1982

Benign teratoma of the Fallopian tube.

Teratoma of the Fallopian tube is very uncommon. Only 47 cases have been reported since 1865. Many have been discovered incidentally and none has been diagnosed preoperatively. The majority are cystic, show great variation in size, are commonly located in the ampulla or isthmus and are either intraluminal or attached to the luminal surface by a pedicle. Histologically they are similar to teratomas of the ovary and elsewhere. Only one instance of malignant tubal teratoma has been recorded. An association with nulliparity or reduced parity has been noted in some cases. The present case of benign tubal teratoma is the 48th and apparently the smallest reported.

Fallopian Tube Neoplasms↗
PubMed1982

Basophil degranulation induced by cigarette smoking in man.

There is some evidence that histamine could be a mediator of the immediate broncho-constriction that follows cigarette smoking. Since the chief reservoir of histamine in normal human blood is the basophil, we studied the acute effects of cigarette smoking on these cells. Capillary blood samples were obtained from 27 healthy young male smokers, before and 10 minutes after smoking. Basophils were collected and concentrated from these samples by a millipore membrane filter technique, stained with toluidine blue, and classified according to the staining characteristics and location of their cytoplasmic granules. This classification differentiated the "intact" from the "degranulated" basophils. A significant increase in degranulated cells and decrease in intact cells (p less than 0.001) was observed after smoking. Since histamine is present in the basophil granules, these findings suggest that cigarette smoking causes histamine release.

Adult↗
PubMed1982

Mast cell density in isolated monkey lungs on exposure to cigarette smoke.

The density and percentage of degranulated cells of the mast cell population were studied in the isolated lungs of 25 monkeys (Macaca radiata radiata) before and after acute exposure to cigarette smoke. In each animal one lung was used as the test lung while the other lung was used as its control. In the control lungs the total mean mast cell count was 9.5/mm2 and the proportion of degranulated cells was 9.7%. In the lungs exposed to smoke the total counts were lower (7.3/mm2) and the percentage of degranulated cells higher (15.8%). These differences were statistically significant (p less than 0.01) and show that after acute exposure to cigarette smoke there is a degranulation of lung mast cells. Since degranulation is accompanied by local release of histamine, which could act on the smooth muscle of the airways, it is suggested that this may be a mechanism by which smoking-induced acute bronchoconstriction is mediated.

Animals↗
PubMed1981

Histamine, theophylline and tryptamine transport through lipid bilayer membranes.

Diffusion of histamine, theophylline and tryptamine through planar lipid bilayer membranes was studied as a function of pH. Membranes were made of egg phosphatidylcholine plus cholesterol (1 : 1 mol ratio) in tetradecane. Tracer fluxes and electrical conductances were used to estimate the permeabilities to nonionic and ionic species. Only the nonionic forms crossed the membrane at a significant rate. The membrane permeabilities to the nonionic species were: histamine, 3.5 x 10(-5) cm x s-1; theophylline, 2.9 x 10(-4) cm x s-1; and tryptamine, 1.8 x 10(-1) cm x s-1. Chemical reactions in the unstirred layers are important in the transport of tryptamine and theophylline, but not histamine. For example, as pH decreased from 10.0 to 7.5 the ratio of nonionic (B) to ionic (BH+) tryptamine decreased by 300-fold, but the total tryptamine permeability decreased only 3-fold. The relative insensitivity of the total tryptamine permeability to the ratio, [B]/[BH+], is due to the rapid interconversion of B and BH+ in the instirred layers. Our model describing diffusion and reaction in the unstirred layers can explain some 'anomalous' relationships between pH and weak acid/base transport through lipid bilayer and biological membranes.

Biological Transport↗
PubMed1981

Hydroxyl ion permeability of lipid bilayer membranes.

The OH- permeability of lipid bilayer (egg phosphatidylcholine-cholesterol) membranes was estimated from ionic transference numbers and membrane conductances at high pH. Membranes are slightly cation (Na+) selective over the pH range of 6--10. However, at pH greater than 11, Na+ and Cl- conductances decrease and OH- conductance increases so that the membrane becomes highly selective to OH-. From the OH- conductance we estimate the OH- permeability coefficient to be 1.8 . 10(-9) cm . s-1. The OH- selectivity of lipid bilayers may contribute to the observed H+/OH- selectivity of some biological membrane at high pH.

Chlorides↗
PubMed1981

Hydrofluoric and nitric acid transport through lipid bilayer membranes.

Hydrofluoric and nitric acid transport through lipid bilayer membranes were studied by a combination of electrical conductance and pH electrode techniques. Transport occurs primarily by nonionic diffusion of molecular HF and HNO3. Membrane permeabilities to HF and HNO3 ranged from 10(-4) to 10(-3) cm . s-1, five to seven orders of magnitude higher than the permeabilities to NO-3, F- and H+. Our results are consistent with the hypothesis that F- transport through biological membranes occurs mainly by nonionic diffusion of HF. Our results also suggest that of the two principal components of 'acid rain', HNO3 may be more toxic than H2SO4.

Cholesterol↗
PubMed1981

Transport of protons and hydrochloric acid through lipid bilayer membranes.

Transport of protons and hydrochloric acid through lipid bilayer membranes was studied by a combination of electrical conductance and pH electrode techniques. In the presence of large pH gradients, proton transport occurs primarily by diffusion of molecular HCl. The permeability of egg phosphatidylcholine/decane bilayers to HCl is about 3 cm . s-1, seven to nine order of magnitude higher than the permeability to H+, OH- or Cl-. The HCl permeability of phosphatidylserine or egg phosphatidylcholine/cholesterol (1 : 1) bilayers is about 50% lower than the permeability of egg phosphatidylcholine bilayers. Diffusion of molecular HCl may be an important process in tissues exposed to high HCl concentrations, e.g., gastric mucosa. However, at neutral pH the diffusion of molecular HCl is too slow to contribute significantly to net movements of H+ or Cl-.

Biological Transport↗
PubMed1981

Genetic studies of H group plasmids by bacteriophage P1 transduction.

Bacteriophage P1 transduction was used to study the incompatibility group H1 plasmid pRG1251, molecular weight 120 x 10(6), and the incompatibility group H2 plasmid pSD114, molecular weight 166 x 10(6). The order of resistance (R) determinants on pSD114 was deduced from transduction and segregation experiments to be chloramphenicol-tetracycline-kanamycin-streptomycin. Resistance to tellurium and to coliphages, which are properties also encoded by many H2 plasmids, were not transduced with the other markers. On pRG1251, the ampicillin and tetracycline resistance markers appear to be located together, as do the chloramphenicol, streptomycin, and sulfamethoxazole resistance markers. Frequently, blocks of R determinants were transposed to the P1 genome or to the Escherichia coli chromosome. P1 DNA was isolated which carried the chloramphenicol, streptomycin, and sulfamethoxazole markers from pRG1251 and had a molecular weight of 64 x 10(6). Other P1 prophages carried R determinants from pSD114 and had molecular weights of 86 x 10(6). A plasmid of molecular weight 124 x 10(6) was also isolated which contained incompatibility determinants from P1 (incompatibility group Y) and from the H2 group plasmid. The mechanism of formation of these unusual plasmid species is discussed.

Anti-Bacterial Agents↗
PubMed1981

Magnesium and membrane function in vascular smooth muscle.

Since a tight electromechanical coupling exists in vascular smooth muscle, even small shifts of the membrane potential are sufficient to change the vascular lumen. The extracellular H+ and K+ concentrations are important effectors for the adjustment of the membrane potential. The ion concentrations in the immediate neighbourhood of the cell membrane can be influenced by the microdynamic binding properties of the basement membrane and the other vascular connective tissue. These structures are polyanionic macromolecules to which mono- and divalent cations are extensively bound, and which are separated from the vascular smooth muscle cell membranes by tiny cleft spaces. The ion binding properties of vascular connective tissue were therefore studied in dependence on proton and cation concentration. The pH-dependent binding of monovalent cations to vascular connective tissue is dependent on the concentration and affinity constant of the ion species in question. The mode of interaction is competition. For instance, the actual K binding characteristic means that an increase of [K+]o close to the cell membrane cold ensue from a diminished K+ binding ability under alkalosis. Depolarization and contraction of vascular smooth muscle cells result. Divalent cation binding to vascular connective tissue it additionally dependent on conformational changes. Already physiological concentrations of Mg++ ions can induce a specific change in configuration, which enables K+ ions to bind cooperatively. This means that with extracellular Mg++ deficiency not only less Mg++ ions are bound to vascular connective tissue but also less K+ ions. [K+]o would increase near the cell membrane, depolarization and vasoconstriction would occur.

Animals↗
PubMed1981

[How large is the tocopherol accumulation capacity of organs? Long term trials with various high oral alpha-tocopherol doses administered to rats and guinea pigs].

Accumulation of Tocopherol in Various Organs. 1. The influence of different doses of vitamin E on the absorption and accumulation of tocopherol in blood and various organs was studied in long time feeding experiments with male guinea pigs (Pirbright White W 58) and male Sprague Dawley rats. The experiment with guinea pigs lasted 32 weeks, that with rats 46 weeks. Three groups of 20 animals of each species were fed semisynthetic diets containing 0.003 g (Gr. I = control), 0.203 g (Gr. II) and 1.009 g (Gr. III) D, L-alpha-tocopherol acetate per 100 g diet. The ratio of tocopherol contents in the diets was 1:100:500. 2. The tocopherol excretion in the faeces increased significantly according to the vitamin E intake; the absorption rate of tocopherol behaves inversely proportional to the level of supply. 3. The tocopherol concentration in blood serum, liver, heart and adrenals of animals of the Groups II and III increased significantly in comparison with the control animals. The tocopherol accumulation in blood and the analysed organs depends on species and is organ specific: Organs of rats of the control group contain higher levels of alpha-tocopherol compared with those of the corresponding group of guinea pigs. According to the relative accumulation capacity of the organs for vitamin E (I:II:III) following sequences can be considered: Guinea pigs: adrenals and heart, liver, blood; rats: liver, heart, blood, adrenals. 4. The tocopherol accumulating organs are of limited capacity. The ratio of the tocopherol intake (1:100:500) could not be found in any of the analysed organs.

Administration, Oral↗
PubMed1980

On the structure of the hemocyanin channel in lipid bilayers.

Keyhole limpet hemocyanin has been shown by others (Alvarez, O., Diaz, E. and Latorre, R. (1975) Biochim. Biophys. Acta 389, 444-448) to form single conductance channels in black lipid membranes. In an attempt to visualize how the large (300 A) water-soluble hemocyanin molecule interacts with lipid bilayers, we have examined hemocyanin in the presence of lipids with the electron microscope. We find that incubation of lipids with keyhole limpet hemocyanin produces a characteristic 70 A in diameter, ring-shaped particle or annulus associated with the bilayer. This annulus, which appears to be quite distinct from previously observed aggregated and dissociated forms of hemocyanin, may be responsible for the channel formation in black lipid membranes.

Animals↗