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Biomedical subjects

S McLaughlin

Publications and source records attributed to S McLaughlin.

At least 127 records · Page 7Linked to original sources
PubMed1981

The adsorption of divalent cations to phosphatidylglycerol bilayer membranes.

The ability of Stern equation to describe the adsorption of divalent cations to phosphatidylglycerol membranes was tested by combining 31P-NMR and electrophoretic mobility measurements. In 0.1 M sodium chloride both the 31P-NMR and the zeta potential data are well described by the Stern equation. 31P-NMR and 13C-NMR results indicate that cobalt forms inner-sphere complexes only with the phosphate group of phosphatidylglycerol molecules and that a substantial fraction of the adsorbed cobalt ions form outer-sphere complexes. Evidence is presented that suggests the alkaline earth cations also bind to phospholipids mainly by forming outer sphere complexes. Electrophoretic mobility measurements were performed with several different divalent cations. In all cases the zeta potentials in 0.1 M sodium chloride were well described by the Stern equation. The intrinsic 1:1 association constants (M-1) for the phosphatidylglycerol complexes decreased in the sequence: Mn2+, 11.5; Ca2+, 8.5; Ni2+, 7.5; Co2+, 6.5; Mg2+, 6.0; Ba2+, 5.5 and Sr2+, 5.0.

Adsorption↗
PubMed1981

The role of electro-osmosis in the electric-field-induced movement of charged macromolecules on the surfaces of cells.

The surfaces of most cells bear a net negative charge. The imposition of an electric field parallel to the surface of the cell should produce, therefore, an electro-osmotic flow of fluid towards the cathodal side of the cell. Our analysis of a simple model of the cell surface indicates that a negatively charged mobile macromolecule will be swept by this electro-osmotic flow of fluid to the cathodal side of the cell if its zeta potential, zeta 1, is less negative than the zeta potential of the cell surface, zeta 2. Conversely, if zeta 2 is less negative than zeta 1, the negatively charged macromolecule will accumulate at the anodal side of the cell. Our experimental results demonstrate that concanavalin A (Con A) receptors on embryonic muscle cells normally accumulate at the cathodal side of the cell, but that they can be induced to accumulate at the anodal side of the cell by preincubating the myotubes either with neuraminidase, a treatment that removes negatively charged sialic acid residues, or with the lipid diI, a treatment that adds positive charges to the surface of the cell. Addition of the negatively charged lipid monosialoganglioside (GM1), on the other hand, enhances the accumulation of Con A receptors at the cathodal side of the cell.

Animals↗
PubMed1981

Adsorption of divalent cations to bilayer membranes containing phosphatidylserine.

The Stern equation, a combination of the Langmuir adsorption isotherm, the Boltzmann relation, and the Grahame equation from the theory of the diffuse double layer, provides a simple theoretical framework for describing the adsorption of charged molecules to surfaces. The ability of this equation to describe the adsorption of divalent cations to membranes containing brain phosphatidylserine (PS) was tested in the following manner. Charge reversal measurements were first made to determine the intrinsic 1:1 association constants of the divalent cations with the anionic PS molecules: when the net charge of a PS vesicle is zero one-half of the available sites are occupied by divalent cations. The intrinsic association constant, therefore, is equal to the reciprocal of the divalent cation concentration at which the mobility of a PS vesicle reverses sign. The Stern equation with this association constant is capable of accurately describing both the zeta potential data obtained with PS vesicles at other concentrations of the divalent cations and the data obtained with with vesicles formed from mixtures of PS and zwitterionic phospholipids. Independent measurements of the number of ions adsorbed to sonicated PS vesicles were made with a calcium-sensitive electrode. The results agreed with the zeta potential results obtained with multilamellar vesicles. When membranes are formed at 20 degrees C in 0.1 M NaCl, the intrinsic 1:1 association constants of Ni, Co, Mn, Ba, Sr, Ca, and Mg with PS are 40, 28, 25, 20, 14, 12, and 8 M-1, respectively.

Cations, Divalent↗
PubMed1981

Diffusion of calcium ions in retinal rods. A theoretical calculation.

The Fick diffusion equation is combined with the Langmuir adsorption isotherm and the relevant equations from the Gouy-Chapman theory of the electrical diffuse double layer to demonstrate that the effective diffusion coefficient of calcium ions, both in the cytoplasm of the rod outer segment and within the aqueous space bounded by the disk membrane, should be reduced by a factor of 10-100 because these ions adsorb to phospholipids present in the disk membrane.

Calcium↗
PubMed1979

Adsorption of monovalent cations to bilayer membranes containing negative phospholipids.

The electrophoretic mobilities of multilamellar phosphatidylserine vesicles were measured in solutions containing monovalent cations, and the xi potentials, the electrostatic potentials at the hydrodynamic plane of shear, were calculated from the Helmholtz--Smoluchowski equation. In the presence of 0.1 M lithium, sodium, ammonium, potassium, rubidium, cesium, tetraethylammonium, and tetramethylammonium chloride, the xi potentials were -60, -62, -72, -73, -77, -80, -82, and -91 mV, respectively. Similar results were obtained with phosphatidylglycerol vesicles; different results were obtained with cardiolipin, phosphatidylinositol, and phosphatidic acid vesicles. The phosphatidylserine results are interpreted in terms of the Stern equation, a combination of the Gouy equation from the theory of the diffuse double layer, the Boltzmann relation, and the Langmuir adsorption isotherm. Evidence is presented that suggests the hydrodynamic plane of shear is 2 A from the surface of the membrane in solutions containing the alkali metal cations. With this assumption, the intrinsic association constants of the above monovalent cations with phosphatidylserine are 0.8, 0.6, 0.17, 0.15, 0.08, 0.05, 0.03, and 0 M-1, respectively. The validity of this approach was tested in two ways. First, the xi potentials of vesicles formed from mixtures of phosphatidylserine and a zwitterionic lipid, phosphatidylcholine, were measured in solutions containing different concentrations of sodium. All the data could be described by the Stern equation if the "relaxation" of the ionic atmosphere, which is predicted by classic electrostatic and hydrodynamic theory to occur at low salt concentrations and high potentials, was circumvented by using only large (diameter greater than 13 micrometers) vesicles for these measurements. Second, the fluorescent probe 2-(p-toluidinyl)naphthalene-6-sulfonate was used to estimate the potential at the surface of phosphatidylserine and phosphatidylglycerol vesicles sonicated in 0.1 M NaCl. Reasonable agreement with the predicted values of the surface potential was obtained.

Cations, Monovalent↗
PubMed1979

Gentamicin-resistant Staphylococcus aureus. Emergence in an intensive care nursery.

Gentamicin sulfate--resistant Staphylococcus aureus suddenly appeared in an intensive care nursery in December 1976 and became the dominant Staphylococcus; it accounted for 96% of the isolates by April 1977. All gentamicin-resistant strains were sensitive to amikacin sulfate, but 98% and 49% were resistant to kanamycin sulfate and tobramycin sulfate, respectively. All but one of the gentamicin-resistant strains were sensitive to methicillin sodium. The mechanism of gentamicin resistance appears to be plasmid mediated. Phage typing, used for epidemiologic purposes, also demonstrated that most gentamicin-resistant strains shared susceptibility to phages 29 and 52; however, 13% were completely different, indicating that gentamicin resistance is not solely related to a phage-susceptible factor.

Bacteriophage Typing↗
PubMed1978

The adsorption of divalent cations to phosphatidylcholine bilayer membranes.

Electrophoretic mobility and 31P NMR measurements were combined to test whether the combination of the Henry, Boltzmann and Grahame equations is capable of describing the adsorption of divalent cations of phosphatidylcholine membranes. Cobalt was chosen for this study because, of all the common divalent cations, its effects on the 31P NMR spectrum of phosphatidylcholine membranes are easiest to interpret. Both the 31P NMR data on the adsorption of cobalt and the zeta potential data calculated from the electrophoretic mobility in the presence of cobalt are well described by the combination of these three equations. Electrophoretic mobility measurements were also performed with a number of other divalent cations and the zeta potentials were, in all cases, well described by the combination of these three equations. The binding deduced from such measurements decreases in the sequence: Mn2+, Mg2+, Ca2+, Co2+, Ni2+, Sr2+, Ba2+. If we assume that a lipid molecule occupies an area of 60 A2 and that there is a 1 : 1 stoichiometry for the binding of the divalent ions to phosphatidylcholine, the dissociation constants are, respectively: 0.3, 1.0, 1.0, 1.2, 1.2, 2.8, 3.6 M.

Adsorption↗
PubMed1978

Haemophilus meningitis in Portsmouth.

The clinical features and follow-up data of all twenty-five children admitted to a Portsmouth hospital from Jan. 1, 1972, to July 1, 1975, with haemophilus meningitis were reviewed. Two children died of meningitis and one of other causes. Four have residual damage--two severe, one definite, and one possible. Outcome tended to be worse in cases with the following features: age less than 9 months at the time of illness, difficult diagnosis, antibiotic treatment before admission, combined treatment with chloramphenicol and ampicillin, and difficulties at home. The continuing high morbidity indicates that children with this disease need careful follow-up.

Age Factors↗
PubMed1978

Electrostatic interactions among hydrophobic ions in lipid bilayer membranes.

We have shown that the absorption of tetraphenylborate into black lipid membranes formed from either bacterial phosphatidylethanolamine or glycerolmonooleate produces concentration-dependent changes in the electrostatic potential between the membrane interior and the bulk aqueous phases. These potential changes were studied by a variety of techniques: voltage clamp, charge pulse, and "probe" measurements on black lipid membranes; electrophroetic mobility measurements on phospholipid vesicles; and surface potential measurements on phospholipid monolayers. The magnitude of the potential changes indicates that tetraphenylborate absorbs into a region of the membrane with a low dielectric constant, where it produces substantial boundary potentials, as first suggested by Markin et al. (1971). Many features of our data can be explained by a simple three-capacitor model, which we develop in a self-consistent manner. Some discrepancies between our data and the simple model suggest that discrete charge phenomena may be important within these thin membranes.

Bacteria↗
PubMed1977

The kinetic mechanism of action of an uncoupler of oxidative phosphorylation.

The chemiosmotic hypothesis predicts that the mechanism by which weak acids uncouple oxidative phosphorylation in mitochondria is identical to the mechanism by which they transport hydrogen ions across artificial bilayer membranes. We report here the results of a kinetic study of uncoupler-mediated hydrogen ion transport across bilayer membranes. We made electrical relaxation measurements on black lipid membranes exposed to the substituted benzimidazole 5,6-dichloro-2-trifluoromethylbenzimidazole. The simplest model consistent with our experimental data allowed us to deduce values for adsorption coefficients and rate constants. Our major conclusions are that the back diffusion of the neutral species is the rate limiting step for the steady state transport of hydrogen ions, that both the neutral and charged forms of the uncoupler adsorb strongly to the interfaces, and that the reactions at the membrane-solution interfaces occur sufficiently rapidly for equilibrium to be maintained. Independent measurements of the adsorption coefficients of both the neutral and anionic forms of the weak acid and also of the permeability of the membrane to the neutral form agreed well with the values deduced from the kinetic study.

Benzimidazoles↗
PubMed1977

Graphological signs for extraversion.

Graphological signs of extraversion were rated from handwriting samples of undergraduates (ns = 35 males, 31 females; 23 males, 20 females) and correlated with extraversion scores from an objective psychological test. No evidence was found for the validity of the graphological signs.

Adolescent↗
PubMed1976

The hydrophobic adsorption of charged molecules to bilayer membranes: a test of the applicability of the stern equation.

To describe the hydrophobic adsorption of charged molecules to bilayer membranes, one must recognize that the adsorption produces a change in the electrostatic potential at the surface of the membrane. The surface potential produced by the adsorption of the charged molecules can be described most simply by the Gouy equation from the theory of the diffuse double layer. This potential will tend to lower the concentration of the adsorbing ions in the aqueous phase immediately adjacent to the membrane, a phenomenon which can be described by the Boltzmann relation. The number of adsorbed ions is, in turn, a function of the aqueous concentration of these ions at the membrane solution interface and can be described, in the simplest case, by a Langmuir adsorption isotherm. If the ions are regarded as point charges, the combination of the Gouy, Boltzmann, and Langmuir relations may be considered a simplified Stern equation. To test experimentally the applicability of this equation, one should measure both the charge density and surface potential as a function of the concentration of adsorbing molecules in the bulk aqueous phases. Direct, accurate measurements of one of these parameters, the number of moles of 2, 6-toluidinylnaphthalenesulfonate ions bound to vesicles formed from phosphatidylcholine, are available in the literature (Huang, C., and Charlton, J.P. (1972), Biochemistry 11, 735). We estimated the change in the surface potential in two independent ways; by means of conductance measurements with "probe" molecules on planar black lipid membranes and by means of electrophoresis measurements on multilaminar unsonicated vesicles. The two estimates agreed with one another and all of the data could be adequately described by the Stern equation, assuming, at 25 degrees C, a dissociation constant of 2 X 10(-4) M and a maximum number of binding sites of 1/70 A2.

Adsorption↗
PubMed1975

Chaotropic anions and the surface potential of bilayer membranes.

The chaotropic anions perchlorate and thiocyanate adsorb to artificial phospholipid membranes. The negative electrostatic potential they produce at the surface of the membranes was measured by two independent techniques. The conductance produced by neutral carriers of cations and anions was measured to estimate changes in the surface potentials of planar black lipid films and the electrophoretic mobility of phospholipid vesicles was used to monitor changes in the zeta potentials of spherical bilayer membranes. Qualitatively similar results were obtained with the two techniques. The results, moreover, agreed with the change in surface potential produced by these anions at an air water interface, as measured directly with an ionizing electrode (Randles, J. E. B. (1957) Discuss. Faraday Soc. 24, 194-199). The results obtained with artificial bilayers may explain the observation (Wieth, J. O. (1970) J. Physiol. 207, 581-609) that thiocyanate increases the sodium or potassium and decreases the sulfate permeability of erythrocyte membranes.

Anti-Bacterial Agents↗