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P F CURRAN

Publications and source records attributed to P F CURRAN.

16 recordsLinked to original sources
PubMed1965

INTRACELLULAR ELECTRICAL POTENTIALS IN FROG SKIN.

The influence of changes in ionic composition of the bathing solutions on intracellular electrical potentials in frog skin has been examined. When the skin bathed in SO(4) Ringer's solution is penetrated with a microelectrode two approximately equal potential jumps were frequently observed and most experiments were carried out with the electrode located between these steps. Substitution of Cl for SO(4) in the bathing solutions caused a decrease in PD across both the "outer" and "inner" barriers. When the skin was short-circuited an average intracellular potential of -18 mv was found with both Cl and SO(4) Ringer's. With the skin in SO4 Ringer's, decrease in Na concentration of the outside solution caused a decrease in PD between the microelectrode and the outside solution which was approximately the same as the decrease in total skin PD. With SO(4) Ringer's, an increase in K concentration in the inside solution caused a marked decrease in total skin PD. However, only 50 per cent of this change occurred at the inner barrier, between the microelectrode and the inside solution. The remainder of the change occurred at the outer barrier. This observation does not appear to be consistent with the model of the skin proposed by Koefoed-Johnson and Ussing (Acta Physiol. Scand., 1958, 42, 298).

Animals↗
PubMed1964

THE INFLUENCE OF NA CONCENTRATION ON NA TRANSPORT ACROSS FROG SKIN.

The effects of changes in Na concentration of the bathing solutions on some transport and permeability properties of the isolated frog skin have been examined. Rate coefficients for unidirectional Na movements across the two major barriers in the skin have been estimated as functions of Na concentration. The results indicate that the "apparent Na permeability" of the outer barrier of the skin decreases markedly when Na concentration in the outer solution is increased from 7 to 115 mM. The observed saturation of rate of Na transport with increasing Na concentration can be ascribed, in part, to this permeability change rather than to saturation of the transport system itself. Unidirectional Cl flux across the short-circuited skin was not significantly altered by an increase in Na concentration from 30 to 115 mM suggesting that the changes in membrane properties are relatively specific for the Na ion. The results also suggest that the movement of Na across the outer membrane may not be due entirely to simple passive diffusion of free Na ions.

Animals↗
PubMed1963

The effect of Ca and antidiuretic hormone on Na transport across frog skin. II. Sites and mechanisms of action.

A method has been developed for determining unidirectional Na fluxes across the two faces of the transporting cells in the frog skin. The method has been used to investigate the location of the sites at which Ca and anti-diuretic hormone act to alter the rate of active Na transport across the skin. The results have indicated that the primary effect of both agents is on the Na permeability of the outward facing membrane of the cells. Ca decreases and the hormone increases permeability of this barrier. Neither agent appears to have a direct effect on the active transport system itself assuming that it is located at the inner membrane of the cells. The rate of active Na transport is altered as a result of changes in the size of the Na pool in the cells which occur because of changes in the rate of Na entry through the outer membrane. Thus, the results indicate that the Na permeability of the outer membrane plays an important role in controlling the rate of net active Na transport across the skin.

Animals↗
PubMed1963

The effect of Ca and antidiuretic hormone on Na transport across frog skin. I. Examination of interrelationships between Ca and hormone.

Ca added to the solution bathing the outside of isolated frog skin causes a decrease in net Na transport across the skin while antidiuretic hormone (ADH) causes an increase. Possible interrelations between the effects of these agents have been examined. The decrease in Na transport caused by Ca was the same before and after treatment of the skin with ADH and the increase in transport caused by ADH was unaffected by the presence of Ca. The relationship between Ca concentration and degree of inhibition of Na transport was not appreciably altered by ADH. These results indicate that Ca and ADH do not compete but act independently at two different sites and these sites appear to be located on the same barrier to Na movement in the skin. Further, Ca causes a decrease in Cl influx across the short-circuited skin but ADH has no effect on Cl movement, again suggesting that the actions of these agents are independent.

Animals↗
PubMed1962

The effect of calcium on sodium transport by frog skin.

Calcium added to the solution bathing the outside of isolated frog skin caused a reversible decrease in net sodium transport across the skin. At constant sodium concentration, the inhibition of transport increased with increasing calcium concentration, but approached a limiting value. This maximum degree of inhibition was found to depend on sodium concentration; sodium transport could be inhibited by 60 per cent at 96 mM sodium, but by only 18 per cent at 19 mM sodium. The relative effectiveness of a given calcium concentration was also greater the higher the sodium concentration. The unidirectional flux of chloride across the short-circuited skin was decreased by calcium to approximately the same degree as active sodium transport. The results have been interpreted in terms of a relatively non-specific decrease in permeability of the outward facing membrane of the transporting cells. The resulting decrease in sodium permeability apparently causes a decrease in active sodium transport by reducing the availability of sodium to the transporting system.

Animals↗
PubMed1960

Na, Cl, and water transport by rat colon.

Segments of the colon of anesthetized rats have been perfused in vivo with isotonic NaCl solutions and isotonic mixtures of NaCl and mannitol. Unidirectional and net fluxes of Na and Cl and the net fluxes of water and mannitol have been measured. Net water transport was found to depend directly on the rate of net Na transport. There was no water absorption from these isotonic solutions in the absence of net solute transport, indicating that water transport in the colon is entirely a passive process. At all NaCl concentrations studied, the lumen was found to be electrically negative to the surface of the colon by 5 to 15 mv. Na fluxes both into and out of the lumen were linear functions of NaCl concentration in the lumen. Net Na absorption from lumen to plasma has been observed to take place against an electrochemical potential gradient indicating that Na is actively transported. This active Na transport has been interpreted in terms of a carrier model system. Cl transport has been found to be due almost entirely to passive diffusion.

Animals↗
PubMed1960

Calcium and strontium in rat small intestine. Their fluxes and their effect on Na flux.

Studies have been carried out on movements of Ca and Sr ions in rat small intestine, using the in vivo preparation developed by Curran and Solomon (5). In the concentration range of 0 to 25 mM, Sr flux appears to be passive, though restricted. Ca transport may not, however, be ascribed to passive independent movement of these ions since at higher concentrations (12.5 and 25 mM) Ca return from blood to intestinal lumen increases more than expected. An apparent diffusion coefficient of Ca and Sr ions in the membrane has been calculated and the influence of negative charges within the membrane on cation diffusion has been examined in a semiquantitative manner. Both Ca and Sr ions exercise a drastic effect on active Na absorption from intestine and on concomitant passive water movement. From 0 to 1 mM, Ca and Sr ions cause a sharp increase in Na and water efflux from the lumen. This rising phase is interpreted in terms of combination of the divalent cation with the Na carrier system following Michaelis-Menten kinetics. At concentrations higher than 1 mM, the effect of Ca and Sr ions is reversed and Na and water absorption decreases slowly as Ca or Sr concentration is increased. This falling phase is ascribed to a non-specific Ca effect which produces a general "stiffening" of the membrane.

Animals↗
PubMed1960

Na, Cl, and water transport by rat ileum in vitro.

Interrelationships between metabolism, NaCl transport, and water transport have been studied in an in vitro preparation of rat ileum. When glucose is present in the mucosal solution, Na and Cl both appear to be actively transported from mucosa to serosa while water absorption is passive and dependent on net solute transport. Removal of glucose from the mucosal solution or treatment with dinitrophenol, monoiodoacetate, or anoxia inhibits active salt transport and as a result, water absorption is also inhibited. The dependence of water absorption on metabolism can be explained as a secondary effect due to its dependence on active salt transport. The relationship between salt and water transport has been discussed in terms of a model system.

Animals↗
PubMed1957

Ion and water fluxes in the ileum of rats.

Studies have been carried out on the movement of salt and water across the small intestine of the rat. Segments of the ileum of anesthetized rats have been perfused in vivo with unbuffered NaCl solutions or isotonic solutions of NaCl and mannitol. Kinetic analysis of movements of Na(24) and Cl(36) has permitted determination of the efflux and influx of Na and Cl. Net water absorption has been measured using hemoglobin as a reference substance. Water was found to move freely in response to gradients of osmotic pressure. Net water flux from isotonic solutions with varying NaCl concentration was directly dependent on net solute flux. The amount of water absorbed was equivalent to the amount required to maintain the absorbed solute at isotonic concentration. These results have been interpreted as indicating that water movement is a passive process depending on gradients of water activity and on the rate of absorption of solute. The effluxes of Na and Cl are linear functions of concentration in the lumen, but both ions are actively transported by the ileum according to the criterion of Ussing (Acta Physiol. Scand., 1949, 19, 43). The electrical potential difference between the lumen and plasma has been interpreted as a diffusion potential slightly modified by the excess of active Cl flux over active Na flux. The physical properties of the epithelial membrane indicate that it is equivalent to a membrane having negatively charged uniform right circular pores of 36 A radius occupying 0.001 per cent of the surface area.

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