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P F Curran

Publications and source records attributed to P F Curran.

At least 37 records · Page 2Linked to original sources
PubMed1972

Alanine efflux across the serosal border of turtle intestine.

The exit of alanine across the serosal border of the epithelial cells of turtle intestine was measured by direct and indirect techniques. A decrease or an increase in cell Na did not affect the amino acid flux from cell to serosal solution. Cells loaded with Na and alanine did not exhibit any extrusion of alanine when their serosal membranes were exposed to an Na-free medium containing alanine. However, substantial amino acid extrusion was observed across the mucosal cell border under similar conditions. Although alanine flux across the serosal membrane appeared to be Na-independent, it showed a tendency toward saturation as cellular alanine concentration was elevated. The results are consistent with the postulate that the serosal and mucosal membranes of intestinal cells are asymmetrical with respect to amino acid transport mechanisms. The serosal membrane appears to have an Na-independent carrier-mediated mechanism responsible for alanine transport while transport across the mucosal border involves an Na-dependent process.

Alanine↗
PubMed1971

Membrane potentials and ion permeability in a cation exchange membrane.

The nonequilibrium electrical potentials across an artificial membrane bathed by solutions of a single salt have been measured and calculated using the Goldman-Hodgkin-Katz equation and the irreversible thermodynamic equation. The latter equation predicts the observed potential differences over a 2500-fold concentration range, while application of a modified Goldman-Hodgkin-Katz equation leads to difficulties.

Biological Transport↗
PubMed1970

The sodium-alanine interaction in rabbit ileum. Effect of sodium on alanine fluxes.

The model of the interaction between Na and alanine at the mucosal border of rabbit ileum has been tested further by examining the efflux of alanine from the cells toward the mucosal solution. Alanine efflux shows a tendency toward saturation as cellular alanine concentration increases and is influenced by cellular Na concentration. A decrease in cell Na concentration causes an increase in the apparent Michaelis constant with little change in maximal efflux rate. Studies on strips of mucosa treated with ouabain or cyanide showed that the direction of net alanine transfer between the cells and the medium is determined by the direction of the Na concentration difference. The cells extrude alanine against a concentration difference when cell [Na] exceeds medium [Na] and accumulate alanine when cell [Na] is less than medium [Na]. The observations are consistent with the model previously suggested involving a transport site that combines with and translocates both Na and alanine, and with the concept that the Na concentration difference between mucosal solution and cytoplasm provides at least part of the energy for active transport of alanine.

Alanine↗
PubMed1970

The sodium-alanine interaction in rabbit ileum. Effect of alanine on sodium fluxes.

The interaction between Na transfer and alanine transfer across the mucosal border of rabbit ileum has been studied further by examining the effect of alanine on Na movement. Studies on strips of mucosa treated with ouabain showed that net Na movements against a Na concentration difference could be caused by a concentration difference of alanine. Na extrusion from mucosal cells was demonstrated when cellular alanine concentration exceeded that in the external medium. Conversely, the cells took up Na against a concentration difference when external alanine concentration was greater than cellular concentration. Unidirectional Na efflux from the cells toward the mucosal solution was increased by loading the cells with alanine. The relation between the increment in Na efflux and alanine efflux was approximately that predicted by the model of Curran et al. (reference 2) for the Na-alanine interaction at the mucosal border of the cells. The results offer further indication that the transport system is reversible and symmetrical.

Alanine↗
PubMed1970

Direct measurement of uptake of sodium at the outer surface of the frog skin.

A combination of the methods described by Schultz et al. (6) and by Ussing and Zerahn (9) was used to measure directly the unidirectional uptake of sodium from the outside solution into the frog skin, under short-circuit conditions. The sodium uptake was determined at six sodium concentrations ranging from 3.4 to 114 mM. NaCl was replaced by choline chloride in the solutions bathing both sides of the skin. Sodium uptake is not a linear function of sodium concentration but appears to be composed of two components, a saturating one and one that varies linearly with concentration. The sodium uptake is inhibited by the addition of lithium to the outside solution. The effect appears to be primarily on the saturating component and has the characteristics of competitive inhibition. In addition, lithium uptake by the skin is inhibited by sodium. The effects of lithium cannot be ascribed to changes in electrical potential difference. Measurements with microelectrodes indicate that under short-circuit condition there is no change in the intracellular potential when lithium chloride is added to the outside solution.

Animals↗
PubMed1970

Dicarboxylic amino acid influx across brush border of rabbit ileum. Effects of amino acid charge on the sodium-amino acid interaction.

Glutamate and aspartate influxes across the brush border of rabbit intestine are saturable processes that are subject to competitive inhibition and are markedly influenced by the Na concentration in the mucosal solution. Lowering the Na concentration increases the amino acid concentration needed to elicit a half-maximal influx but does not significantly affect the maximal influx. The interaction between Na and anionic amino acid influx can be described by the same kinetic model that has been applied to the influxes of neutral amino acids and lysine. Comparison of the kinetic parameters for anionic, neutral, and cationic amino acids suggests that amino acid charge influences (a) the stability of the binary (amino acid-site) complex and (b) the affinity of this binary complex for the subsequent binding of Na. A mechanistic interpretation of these interactions is proposed.

Animals↗
PubMed1970

Characteristics of the amino acid transport system in the mucosal border of rabbit ileum.

The specificity of the neutral amino acid transport system in the brush border was examined by studying the ability of amino acid analogues to inhibit the unidirectional influx of phenylalanine from mucosal solution into the cells. Effects were evaluated in terms of the affinity of various substrates for the amino acid site in the transport system. The affinity of amino acids for the site was proportional to the number of carbon atoms in the side chain. Electron-withdrawing substituents in the ring of phenylalanine increased affinity and electron-releasing groups decreased affinity. Removal of the alpha-amino group from phenylalanine decreased affinity by a factor of approximately 50 and removal of the carboxyl group decreased affinity 12-fold. Effects on affinity of variations in the side chain of the amino acid can be comparable in magnitude to that of the carboxyl group. The effect of sodium ion on the transport system appears to be similar for all compounds tested.

Amidines↗
PubMed1969

Sodium and sugar fluxes across the mucosal border of rabbit ileum.

Unidirectional influxes of sugars and Na from muscosal solution into the cells of rabbit ileum have been examined. The influxes of glucose, galactose, and 3-0-methyl glucose (3 MG) follow Michaelis-Menten type kinetics and are markedly dependent on the presence ofNa in the mucosal solution. For 3 MG, reduction of Na concentration causes a decrease in maximal rate of influx and little change in the "apparent Michaelis constant." There appeared to be little mediated entry of 3 MG into the cells from Na-free solution. The influx of Na was increased by the presence of 3 MG in the mucosal solution and at all Na concentrations tested, there was a 1:1 ratio between sugar influx and the sugar-dependent Na influx. On the basis of these observations, a model has been developed for the sugar transport system involving a transport site that combines with both sugar and Na.

Animals↗