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Biomedical subjects

M D White

Publications and source records attributed to M D White.

At least 73 records · Page 4Linked to original sources
PubMed1986

Onchocerciasis in Sierra Leone. I. Studies on the prevalence and transmission at Gbaiima village.

A longitudinal survey--parasitological, clinical, immunological and entomological--of onchocerciasis is being conducted in Gbaiima village in Sierra Leone. The estimated Annual Transmission Potential (ATP) is 5863. More than 80% of the annual transmission occurs between October and December. Four species of the Simulium damnosum complex are known to breed in a nearby river. The relative role of these species as vectors has yet to be determined. The total population (598 persons) aged one year and over were examined. Based on microfilarial and nodular rates the prevalence of onchocerciasis was 68.6%. In persons above 15 years of age this prevalence was 88.9%. Microfilarial and nodular rates were related to age. Severe skin lesions occurred in 1.0% of persons. 24 adults (7.5%) were blind (but the cause of the blindness was not determined).

Adolescent↗
PubMed1985

Pathogenetic mechanisms of nephrotoxicity: insights into cyclosporine nephrotoxicity.

Drugs may produce acute renal failure by prerenal, intrarenal and obstructive (postrenal) mechanisms. Prerenal processes usually develop from an imbalance of the normal counterbalancing vasoconstrictor and vasodilatory substances regulating RBF, resulting in a predominant vasoconstrictive state. Intrarenal processes develop from toxic renal tubule epithelial cell injury. The pathogenesis of renal cell injury is a complex interplay among derangements in subcellular membrane functions and mediators of injurious processes. Plasma and subcellular membrane injury and resulting membrane dysfunction appear most important. Cyclosporine has the ability to interact with renal tubular cell membranes in a relatively specific manner and at low concentrations. Despite this interaction, the acute declines in renal excretory function produced by cyclosporine is due predominantly to functional declines in RBF rather than structural derangements in renal tubular cell integrity. Cyclosporine-induced acute renal failure, thus, appears to be due predominantly to prerenal, rather than intrarenal, processes in the experimental animal. Cyclosporine does, however, possess a limited toxic potential to injure renal cortical cells, so that a chronic tubulointerstitial nephropathy may develop with long-term use of this immunosuppressive agent.

Acute Kidney Injury↗
PubMed1984

Pore properties of the Golgi membrane from lactating-rat mammary gland. Effects of pH and temperature and reconstitution into phospholipid vesicles.

Golgi-membrane vesicle penetration was studied by osmotic lysis. Pronounced temperature dependence of mannitol and mannoheptitol penetration over 0-37 degrees C gave linear Arrhenius plots, with activation energies of 75 and 117 kJ/mol respectively. Glucose penetration was constant over pH 5-9, but was respectively faster and slower at higher and lower pH values. Solubilized, dialysed, heat-stable extracts of Golgi membrane were reconstituted into egg yolk phospholipid membranes with apparent recovery of specific permeability. Penetration is interpreted in terms of a pore, for which the Renkin equation predicts a radius of about 0.54 nm.

Animals↗
PubMed1984

Dantrolene and calcium uptake by the sarcoplasmic reticulum of malignant hyperpyrexia-susceptible pigs.

Sarcoplasmic reticulum membranes were isolated from the skeletal muscle of pigs susceptible or resistant to the anaesthetic complication malignant hyperpyrexia. The skeletal muscle relaxant dantrolene was shown to be without effect on the Ca2+ -dependent ATPase activity of either sarcoplasmic reticulum preparation. The active transport of calcium by sarcoplasmic reticulum from both sources was also unaffected by the presence of dantrolene. These findings indicate that dantrolene does not exert its pharmacological action in skeletal muscle by stimulating calcium uptake by the sarcoplasmic reticulum.

Adenosine Triphosphatases↗
PubMed1983

The effect of dantrolene on skeletal-muscle sarcoplasmic-reticulum function in malignant hyperpyrexia in pigs.

The effect of the muscle relaxant dantrolene on isolated sarcoplasmic reticulum was studied in control and malignant-hyperpyrexia-susceptible Landrace pigs. The membranes prepared from both sources showed similar Ca2+-dependent ATPase activities, had comparable phospholipid/protein ratios, and their sodium dodecyl sulphate/polyacrylamide-gel patterns were indistinguishable. Membranes from both sources appeared to bind similar amounts of dantrolene. The drug did not stimulate Ca2+-dependent ATPase activity in preparations from either source. The rates of Ca2+ exchange and Ca2+ efflux appeared to be similar in sarcoplasmic reticulum of control and malignant-hyperpyrexia-susceptible pigs. Dantrolene did not affect either the rates or the amount of Ca2+ lost from the vesicles. These results suggest that dantrolene does not directly affect the movement of Ca2+ across the sarcoplasmic-reticulum membrane.

Animals↗
PubMed1983

A novel method for the isolation of calsequestrin from porcine skeletal muscle sarcoplasmic reticulum.

Calsequestrin was selectively solubilized from porcine skeletal muscle sarcoplasmic reticulum by incubation with HgCl2 and deoxycholate. While deoxycholate alone caused non-specific solubilization of calsequestrin and other extrinsic proteins, HgCl2 alone failed to extract significant amounts of extrinsic proteins. The simultaneous presence of HgCl2 and deoxycholate was necessary for the selective and quantitative solubilization of calsequestrin. Following DEAE-Sephadex ion-exchange chromatography of the HgCl2/ deoxycholate-solubilized material, calsequestrin was obtained in nearly homogeneous form. Porcine calsequestrin was similar to rabbit calsequestrin with respect to its amino acid composition and apparent molecular weight as determined by SDS-polyacrylamide gel electrophoresis. The calcium-binding capacity of porcine calsequestrin was 400 nmol of Ca2+ bound/mg protein, lower than the values reported for the rabbit protein.

Amino Acids↗
PubMed1982

Biosynthesis of galactinol by lactose synthetase.

1. myo-Inositol was galactosylated by UDP-galactose in the presence of alpha-lactalbumin plus rat mammary Golgi membranes enriched in galactosyltransferase (EC 2.4.1.22). 2. The isolated product migrated on GLC as two peaks of material, apparently identical to galactinol (galactosylinositol) isolated from rat milk. 3. These findings make it likely that in vivo lactose synthetase is responsible for converting inositol into galactinol within the Golgi lumen. 4. This is consistent with the ability of inositol to penetrate the Golgi membrane in vitro, and renders less likely a previously proposed role of beta-galactosidase (EC 3.2.1.23) in mammary galactinol synthesis.

Animals↗
PubMed1981

Composition, stability and electrolyte permeability of Golgi membranes from lactating-rat mammary gland.

1. Golgi membrane vesicles, isolated from lactating-rat mammary gland and greatly enriched in galactosyltransferase (EC 2.4.1.22), contained over 40 separate bands of protein, including some periodic acid)(Schiff-staining material and free thiol groups, when analysed by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. 2. The membrane lipids were enriched in phosphatidylcholine, phosphatidylethanolamine and unesterified cholesterol. 3. Membrane fluidity, as monitored by the fluorescence polarization of 1,6-diphenylhexa-1,3,5-triene, increased linearly over 5-37 degrees C. 4. The vesicle membranes were impermeable to lactose over a wide pH range, but admitted electrolytes of molecular weight below about 300. 5. These properties are discussed with respect to other cellular membranes and the secretion of milk products.

Animals↗
PubMed1981

Mannitol and glucose movement across the Golgi membrane of lactating-rat mammary gland.

1. Purified Golgi-membrane vesicles of lactating-rat mammary gland were penetrated by glucose. 3-O-methylglucose, mannose, fructose, sorbitol and mannitol, but not by lactose or sucrose. 2. The kinetics of mannitol uptake and release were followed at 2-6 degrees C with the aid of fine filters (0.45 micrometers pore size) to separate the vesicles from the medium. 3. Mannitol efflux exhibited apparent first-order kinetics with k approximately 1 min-1. Neither saturability, nor inhibition by excess sorbitol or glucose, could be observed. 4. Mannitol efflux at 18 degrees C was about seven times faster than at 1 degrees C, and rates at higher temperatures were too fast to be measured. The rate of glucose efflux at 2-6 degrees C exceeded that of mannitol severalfold. 5. These findings imply a channel or carrier of definite, but limited, specificity straddling the Golgi membrane and able to supply glucose for lactose synthesis.

Animals↗
PubMed1980

Permeability of lactating-rat mammary gland Golgi membranes to monosaccharides.

The Golgi-membrane vesicles present in particulate preparations of lactating rat mammary gland were biosynthetically loaded with [14C]lactose. This lactose was effectively retained by particles sedimented after exposure to 0.25 M-disaccharide, but was partly lost after exposure to 0.25 M-glucose or other solutes of similar size. Loss of lactose was time-, concentration- and temperature-dependent and varied with the solute structure. This behaviour is ascribed to the presence of protein in the Golgi membrane, forming a specific carrier or channel that serves to supply glucose for lactose synthesis.

Animals↗
PubMed1980

A water-extractable Ca2+-atpase from erythrocyte membranes.

The Ca2+- and Mg2+-stimulated ATPase activities present in low ionic strength extracts of erythrocyte membranes have been separated from each other. The Ca2+-ATPase appears to be associated with particulate meterial which could be sedimented by high-speed centrifugation. The pellet obtained was composed mainly of components 1, 2, 4.5, 5 and 7. A soluble protein from the band 3 region, known to be responsible for the Mg2+-ATPase activity, was not detected in this pellet.

Adenosine Triphosphatases↗
PubMed1980

Purification of a water-soluble Mg2+-ATPase from human erythrocyte membranes.

A water-soluble Mg2+-ATPase previously reported (White, M.D. and Ralston, G.B. (1976) Biochim. Biophys. Acta 436, 567-576) has been purified from human erythrocyte membranes. The purified enzyme has a molecular weight of 575 000; the apparent minimum molecular weight was 100 000, corresponding to a soluble protein of the component 3 region. The Km value for ATP was 1 mM and apparent Km for Mg2+ was 3.6 mM. By means of histochemical activity staining in acrylamide gels it was shown that the purified ATPase preparation could be inhibited by Cd2+ and Zn2+ salts, p-chloromercuribenzoate and N-ethylmaleimide, known inhibitors of membrane endocytosis.

Adenosine Triphosphatases↗
PubMed1979

The 'hollow cylinder' protein of erythrocyte membranes.

The 'hollow cylinder' protein (Harris, J.R. (1968) Biochim. Biophys. Acta 150, 534-537) has been purified from human erythrocyte membranes. The molecular weight of the native protein, as determined by analytical ultracentrifugation, was found to be 747,000. By means of sodium dodecyl sulphate gel electrophoresis, the purified protein was shown to be composed of three different low molecular weight polypeptides of average molecular weight 25,000. This study provides convincing evidence that the spectrin tetramer is not responsible for the characteristic electron microscopic appearance of the hollow cylinder protein.

Electrophoresis, Polyacrylamide Gel↗