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Biomedical subjects

A R Chipperfield

Publications and source records attributed to A R Chipperfield.

At least 37 records · Page 2Linked to original sources
PubMed1981

Chloride dependence of frusemide- and phloretin-sensitive passive sodium and potassium fluxes in human red cells.

1. In outdated human red blood cells, there was a Ko-dependent, ouabain-insensitive efflux of Na that was inhibited by frusemide and phloretin. 2. It was reduced or absent (a) in media containing Ca or Mg, (b) in fresh cells. 3. In media with Cl partly replaced by NO3, Na efflux, and its sensitivity to Ko and frusemide, were reduced. 4. The saturable component of ouabain-insensitive K influx was dependent on Cl and inhibited by frusemide and by phloretin. 5. Bromide also supported a frusemide-sensitive, ouabain-insensitive K influx but acetate and SO4 (like NO3) did not.

Biological Transport↗
PubMed1980

An effect of chloride on (Na+K) co-transport in human red blood cells.

In certain conditions, internal K can stimulte active Na:K transport as well as Na:Na exchange through the ouabain-sensitive Na, K exchange pump. When the exchange was examined during a study of the action of internal K, it emerged that the removal of K0 (the main requirement for Na:Na exchange) reduced the ouabain-insensitive Na efflux. Thus, in eight experiments done variously with outdated cells or high and low [K]i, PCMBS-treated cells, the K0-dependent Na efflux ranged from 0.18 to 0.70 muEquiv per ml cells per h. This conflicts with the well established view that the K0-dependent and ouabain-sensitive components of Na efflux are identical. However, the K0-dependent, ouabain-insensitive Na efflux was found to go through the (Na+K) co-transport system, which was further found to show a dependence on chloride ions.

Biological Transport, Active↗
PubMed1979

Separation of the microvillous (maternal) from the basal (fetal) plasma membrane of human term placenta: methods and physiological significance of marker enzyme distribution.

Plasma membranes from normal, full-term human placental trophoblast have been isolated by a new procedure. The method depends upon isopycnic zonal centrifugation using linear sucrose/Ficoll density gradients. Enrichment of plasma membrane marker enzymes with respect to trophoblast homogenate is found in two distinct peaks (designated B and D) of the fractionated effluent recovered from the rotor. Fraction B is enriched with membrane-bound alkaline phosphatase and 5'-nucleotidase, but not with (Na+, K+)-ATPase of F(-)-stimulated adenylate cyclase. It is suggested that this material is derived from the maternal-facing microvillous plasma membrane. Fraction D, enriched with (Na+, K+)-ATPase, F(-)-stimulated adenylate cyclase and, to a smaller extent, with 5'-nucleotidase and alkaline phosphatase is, by exclusion, proposed to be derived from the fetal-facing basal plasma membrane. Both plasma membrane fractions are shown to be free of appreciable contamination, using specific markers for endoplasmic reticulum, mitochondria, nuclei and lysosomes. The separation of the two membrane fractions is shown to depend both upon these membranes forming closed vesicles during homogenization and upon the buoyant densities of such vesicles differing in such a way that microvillous plasma membranes band at a lower density than basal plasma membranes. No separation of the membranes is achieved in gradients in which the vesicles are collapsed.

Alkaline Phosphatase↗
PubMed1976

The connexion between the ion-binding sites of the sodium pump.

1. A study has been made of K influx into human red blood cells in order to determine the influence of internal Na on the affinity of the Na pump for external K. Cells were prepared to contain minimal K and two Na concentrations (about 10 and 30 mueqiv/ml. cells) and incubated in solutions with a range of K concentrations. 2. In choline (Na-free) Ringer, activation of K influx by external K was hyperbolic. The Km for external K increased as the internal Na concentration was raised. The increase was greater than the increase in K influx with saturating external K. The Km for external K increased towards a limiting value as the internal Na concentration was raised. 3. In contrast, in Na-Ringer, the activation by external K was sigmoidal and the affinity for external K was independent of the internal Na concentration. 4. K influx was measured at two submaximal levels of external K with a range of internal Na. The affinity for internal Na fell as external K was raised. 5. The results suggest that in the absence of competition between Na and K on the same side of the membrane, there is a connexion between the ion-binding sites of the Na pump.

Binding Sites↗
PubMed1973

Reconstitution of the sodium pump from protein and phosphatidylserine: features of ouabain binding.

1. A study has been made of ATP splitting and ouabain binding to the sodium pump reconstituted from protein and phosphatidylserine.2. Ouabain was bound to protein alone, but when phosphatidylserine was added, binding was increased threefold. The stimulation resembled the course of activation of sodium-dependent ATPase activity.3. EGTA partly simulated the activation of ATPase by phosphatidylserine but did not enhance binding.4. The dissociation constant for the enzyme-ouabain complex was 3.5 x 10(-8)M. The turnover number (2,000 molecules of ATP per minute) and the number of receptor sites (3.8 x 10(13) per mg protein) were calculated.5. The results provide further evidence of the involvement of phosphatidylserine in the action of the sodium pump.

Adenosine Triphosphatases↗