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Biomedical subjects

J F Aiton

Publications and source records attributed to J F Aiton.

31 records · Page 2Linked to original sources
PubMed1982

K+ transport in "tight' epithelial monolayers of MDCK cells.

Bidirectional transepithelial K+ flux measurements across 'high-resistance' epithelial monolayers of MDCK cells grown upon millipore filters show no significant net K+ flux. Measurements of influx and efflux across the basal-lateral and apical cell membranes demonstrate that the apical membranes are effectively impermeable to K+. K+ influx across the basal-lateral cell membranes consists of an ouabain-sensitive component, an ouabain-insensitive component, an ouabain-insensitive but furosemide-sensitive component, and an ouabain- and furosemide-insensitive component. The action of furosemide upon K+ influx is independent of (Na+ - K+)-pump inhibition. The furosemide-sensitive component is markedly dependent upon the medium K+, Na+ and Cl- content. Acetate and nitrate are ineffective substitutes for Cl-, whereas Br- is partially effective. Partial Cl- replacement by NO3 gives a roughly linear increase in the furosemide-sensitive component. Na+ replacement by choline abolishes the furosemide-sensitive component, whereas Li+ is a partially effective replacement. Partial Na+ replacement by choline abolishes the furosemide-sensitive component, whereas Li+ is a partially effective replacement. Partial Na+ replacement with choline gives an apparent affinity of approximately 7 mM Na, whereas variation of the external K+ content gives an affinity of the furosemide-sensitive component of 1.0 mM. Furosemide inhibition is of high affinity (K1/2 = 3 micrometer). Piretanide, ethacrynic acid, and phloretin inhibit the same component of passive K+ influx as furosemide; amiloride, 4,-aminopyridine, and 2,4,6-triaminopyrimidine partially so. SITS was ineffective. Externally applied furosemide and Cl- replacement by NO3- inhibit K+ efflux across the basal-lateral membranes indicating that the furosemide-sensitive component consists primarily of K:K exchange.

Animals↗
PubMed1981

Occurrence of passive furosemide-sensitive transmembrane potassium transport in cultured cells.

Furosemide (1 x 10(-4) M) inhibits a proportion of the total passive (ouabain-insensitive) K+ influx into primary chick heart cell cultures (85%), BC3H1 cells (75%), MDCK cells (40%) and HeLa cells (57%). This action of furosemide upon K+ influx is independent of (Na+ + K+)-pump inhibition since the furosemide-sensitive component of the K+ influx is identical in the presence and absence of ouabain (1 x 10(-3) M). For HeLa cells the passive, furosemide-sensitive component of K+ influx is markedly dependent upon the external K+, Na+ and Cl- content. Acetate, iodide and nitrate are ineffective as substitutes for Cl-, whereas Br- is partially effective. Partial Cl- replacement by NO3- gave an apparent affinity of 100 mM [Cl]. Na+ replacement by choline+ abolishes the furosemide-sensitive component, whereas Li+ replacement reduces this component by 48%. Partial Na+ replacement by choline+ gives an apparent affinity of 25 mM [Na+]. Variation in the external K+ content gives an affinity for the furosemide-sensitive component of approx. 1.0 mM. Furosemide inhibition of the passive K+ influx is of high affinity, half-maximal inhibition being observed at 5 x 10(-6) M furosemide. Piretanide (1 x 10(-4) M) and phloretin (1 x 10(-4) M) inhibit the same component of passive K+ influx as furosemide; ethacrynic acid and amiloride (both 1 x 10(-4) M) partially so. The stilbene, SITS (1 x 10(-6) M), was ineffective as an inhibitor for the furosemide-sensitive component.

Animals↗
PubMed1981

Down-regulation of the sodium pump following chronic exposure of HeLa cells and chick embryo heart cells to ouabain.

1 HeLa cells and primary cultures of embryonic chick heart cells were grown in medium containing low concentrations of ouabain for 24 h. 2 Compared with normal cells, cells grown in ouabain have fewer free sodium pump sites, an increased intracellular sodium concentration and a decreased intracellular potassium concentration. The cells are able to maintain their intracellular ion contents because the remaining pump sites have an increased turnover rate. 3 When cells that have been chronically exposed to ouabain are returned to normal growth medium, the sodium pump site numbers increase; the recovery process begins within 6 to 8 h and is complete within 24 h. Recovery of pump site numbers is primarily dependent upon de novo protein synthesis since the protein synthesis inhibitor, cycloheximide, prevents recovery.

Animals↗
PubMed1980

The effect of exogenous adenosine triphosphate on potassium movements in HeLa cells.

The effect of exogenous adenosine triphosphate (ATP) on the potassium movements of cultured HeLa cells has been studied. The results obtained were consistent with the hypothesis that, in these cells, externally applied ATP activates a tightly coupled potassium-potassium (K-K) exchange mechanism. The response to ATP was characterized by a transient, 20-fold increase in both the potassium influx and potassium efflux. The tight coupling of the K-K exchange mechanism was confirmed by the results of several different types of experiment, all of which demonstrated the consistent matching of the ATP-stimulated fluxes. Two different strains of HeLa cells gave quantitatively different responses under similar experimental conditions. The reason for this difference was investigated and evidence was obtained which was consistent with the view that the membrane potential also influenced the HeLa cell K-K exchange mechanism.

Adenosine Triphosphate↗
PubMed1979

Potassium permeability of embryonic avian heart cells in tissue culture.

The relationship between the external potassium concentration ([K]o) and membrane permeability has been reexamined using a tissue-cultured preparation of embryonic chick heart cells in which diffusional limitations are minimal. The unidirectional K efflux and electrochemical gradients were determined as a function of [K]o, and the results showed that potassium permeability was constant within the range of 1-20 mM [K]o. Membrane potentials were obtained in K-free solutions and correlated with 42K efflux and intracellular ion content measurements under the same conditions. In contrast to preparations of the intact embryonic chick heart, 42K efflux does not decrease in K-free media. Simulations of tracer measurements at reduced [K]o from naturally occurring cardiac muscle indicate that the experimentally observed decrease in 42K efflux could result from diffusional limitations. This observation, when coupled with the experimental results, suggests that the effect of low [K]o on membrane permeability in homeothermic preparations of cardac muscle should be reevaluated.

Animals↗
PubMed1976

The high molecular weight proteins released from cultured cells.

Studies have been performed with the serum-free culture medium taken from several fibroblast monolayer culture lines. A high molecular weight protein fraction was separated from the concentrated medium by sucrose density gradient centrifugation. Polyacrylamide gel electrophoresis was used to assess the degree of purification obtained. In the electron microscope the negatively stained high molecular weight proteins were found to closely resemble the alpha2-macroglobulins. The suggestion that these proteins from cultured cells resemble the cylindrical protein complex isolated from mammalian erythrocyte ghosts is not supported by this study. The results are discussed in the light of the extensive literature now available on the electron microscopy of high molecular weight proteins.

Blood Proteins↗
PubMedDate not supplied

Cation transport in lymphoblastoid cell lines established from bipolar manic-depressive patients.

Lymphoblastoid cell lines established from patients suffering from bipolar manic depression have been used to study the possible involvement of cation transport in the aetiology of this illness. No significant difference was found in the K+ fluxes mediated by the ouabain-sensitive sodium pump, the diuretic-sensitive cotransport system and the passive leak pathway of cell lines established from either control or bipolar subjects. The mean value for the specific binding of 3H-ouabain (sodium pump site number) was significantly higher in the bipolar group (approximately 30%) than in the control group.

Adult↗