Sodium Transport Pool Research Articles

Aldosterone and thyroid hormone interaction on the sodium and potassium transport pathways of rat colonic epithelium

The effect of hypothyroidism on potassium adaptation (shown by increased potassium secretion in response to potassium loading) and on the action of aldosterone on potassium secretion and sodium fluxes was examined in the rat distal colon. Potassium adaptation, particularly the response to an acute potassium load, was impaired by hypothyroidism which also considerably reduced the rise of transepithelial electrical potential difference (p.d.) of total and transcellular (active) lumen-to-plasma sodium fluxes and of potassium secretion normally produced by aldosterone. These changes were, in part, corrected by a short period (3 days) of tri-iodothyronine replacement. Moreover in aldosterone-treated hypothyroid rats, amiloride in the lumen was considerably less effective in reducing the p.d. and sodium fluxes than in aldosterone-treated normal rats. The intracellular sodium transport pool was greater in the hypothyroid than in the normal rats (5.0 +/- 1.1 (S.E.M.) nmol/mg dry weight compared with 2.9 +/- 0.2 nmol/mg dry weight; P less than 0.02). Aldosterone increased the pool in the normal but not in the hypothyroid rats while amiloride had little effect on the pool in the aldosterone-treated hypothyroid rats but almost abolished it in aldosterone-treated normal rats. Aldosterone plays a major part in the adaptation of colonic sodium and potassium transport to sodium depletion or potassium excess; these adaptations were much impaired in hypothyroid animals. The present results are consistent with a deficiency in aldosterone induction of potassium- and amiloride-sensitive sodium pathways in the apical membrane of colonic epithelial cells in hypothyroid rats, a deficiency which limits the stimulant effect of aldosterone on sodium and potassium transport.

Sodium transport and the cellular sodium transport pool of colonic epithelium: effects of sodium loading, aldosterone and lithium

The cellular sodium transport pool and sodium transepithelial fluxes were investigated in vivo in rat distal colon in relation to sodium loading by intravenous infusion (3.5 h), and to short (4 h) and prolonged (72 h) i.v. administration of aldosterone. Considerable natriuresis and increase in body sodium content were produced by the sodium load but there was no significant effect on the transcellular sodium flux (active absorption from lumen to plasma) or on the sodium transport pool. Both short and prolonged aldosteronism produced similar increases in the transport pool and in the transcellular sodium flux, but the transepithelial electrical potential difference (p.d.) was significantly greater in rats given the prolonged infusion. Addition of amiloride to the solution in the lumen of the colon almost completely abolished the p.d., the transport pool and the transcellular sodium flux of the rats receiving prolonged infusion, but had much less effect in those given the short infusion. The time-course of recovery of p.d. following prolonged aldosteronism was similar to that described for the turnover rate of rat colonic epithelial cells. Lithium within the lumen had no significant effect in untreated rats but after prolonged aldosterone infusion lithium reduced the p.d. and the transcellular sodium flux although the transport pool was not reduced. These findings are consistent with the hypothesis that aldosteronism renders the apical membranes of the epithelial cells permeable to lithium and that intracellular accumulation of lithium depresses active sodium transfer.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of the sodium transport pool in epithelia from tracer fluxes: a simplified approach.

The epithelial content of tracer Na can be calculated either from the exponential increase of unidirectional transepithelial Na tracer fluxes observed after addition of labeled Na to the solution bathing the luminal side of isolated epithelia or from the linear portion of the rate of accumulation of label in the serosal solution. The second method is not only simpler, because fewer data points are required and no logarithmic transformations are necessary, but also more accurate, as shown in experiments with stripped epithelia of rabbit descending colon. From the difference in tissue Na tracer content in the absence and presence of amiloride, which blocks luminal Na uptake, a Na concentration in the transport pool of 8-10 mM is obtained, assuming that all cells participate in active transport. From a comparison of the intracellular Na concentration derived from current-voltage relations of the apical Na entry step with the Na concentration in the epithelial Na transport pool, an estimate may be obtained of what fraction of the cell mass is involved in active Na transport.

Sodium-coupled sugar transport: effects on intracellular sodium activities and sodium-pump activity.

Intracellular sodium activities, (Na)c, were determined in Necturus small intestine before and after addition of galactose to the mucosal bathing solution. In the absence of galactose, (Na)c averaged 12 millimoles per liter. Within 2 minutes after the addition of galactose to the mucosal solution, (Na)c increased to a mean value of 20 millimoles per liter and then declined, in parallel with an increase in transcellular sodium transport, to a value that did not differ significantly from that observed in the absence of the sugar. The final steady state in the presence of galactose was characterized by a three- to fourfold increase in the rate of transcellular Na+ transport in the absence of a significant increase in (Na)c. Thus, the increase in steady-state basolateral pump activity cannot be attributed to an increase in the intracellular sodium transport pool.

Intracellular ion activities in frog skin in relation to external sodium and effects of amiloride and/or ouabain.

Intracellular activities of sodium, potassium and chloride ions, aiNa, aiK, and aiCl were measured with ion-selective single-, double- and triple-barrelled micro-electrodes in skin and isolated epithelia of Rana temporaria bathed on both sides with normal or modified physiological saline. Apical and basolateral membrane potentials, psi ac and psi cs and resistance Ra and Rb respectively were also measured and from the latter the fractional resistance of the apical membrane, F(Ra) and voltage divider ratio, delta psi ac/delta psi cs were measured as criteria of satisfactory membrane penetration by the micro-electrodes. Under control conditions, aiNa was 12.3 +/- 0.8 mM, aiK was 70.3 +/- 22 mM and aiCl was 20.3 +/- 1.6 mM with psi ac averaging -38.0 +/- 3.2 mV. When 10(-4) M-amiloride was added to the apical bathing fluid aiNa fell within 10 min to 1.18 +/- 0.1 mM and aiCl to 5.2 +/- 0.9 mM, while aiK increased to 86.2 +/- 3.8 mM as measured from the basolateral border of isolated epithelia. The sodium transport pool of the skin was measured from the fall in aiNa in the presence of amiloride and could be expressed as 33 X 10(-9) mol cm-2 of epithelium. The mean rate of fall of aiNa under these conditions corresponded to an efflux rate at the basolateral border of 30.1 X 10(-9) mol cm-2 min-1 (48 microA cm-2) giving a half-time for turnover of the sodium transport pool of 33 s. Reduction of sodium concentration in the apical fluid from the normal 79 mM-Na to 10, 1 and 0.1 mM caused aiNa to fall in stages to 2 mM. Because psi ac increased in negativity to -101 mV in the process, this driving force for passive sodium accumulation, more than offset the increased sodium gradient opposing sodium influx across the apical border.

Amiloride sensitive and insensitive sodium pathways and the cellular sodium transport pool of colonic epithelium in rats.

Methods for measurement of the epithelial Na transport pool (Nat) using epithelial scrapings and for analysing the transepithelial ionic fluxes of rat distal colon in vivo into transcellular and paracellular components have been used to study the amiloride sensitive (a.s.) and amiloride insensitive (a.i.) transcellular pathways in relation to variations of Nat. In the Na-replete normal rats, substitution of SO4 for Cl in the lumen approximately halved the Na transported by a.i. pathways and reduced Nat by about 60%, but in the Na-depleted rats, substitution of SO4 did not affect either the Na transported by a.s. pathways or Nat. The value of Nat for normal rats, with 150 mM-NaCl in the lumen, was 6-7 nmol Na mg-1 dry weight (corresponding to about 2-3 mmol kg-1 cell water) and fell by about 60% when lumen Na concentration was reduced to 50 mM. Its turnover half-time was 0.6 min. Nat was about threefold greater in the Na-depleted than in the normal rats but became undetectable when amiloride was in the lumen. Amiloride did not affect Nat in normal rats. We conclude that the increased Na absorption in Na depletion depended on substitution of a.s. for a.i. apical membrane pathways allowing increased Na entry into the epithelial cells so expanding Nat and stimulating the basolateral Na pumps.

Effect of ouabain, amiloride, and antidiuretic hormone on the sodium-transport pool in isolated epithelia from frog skin (Rana temporaria).

When tracer Na+ is added to the solution bathing the apical side of isolated epithelia the observed transepithelial tracer influx increases with time until a steady state is reached. The build-up of the tracer flux follows a single exponential course. The halftime for this build-up under control conditions was 0.92 +/- 0.06 min, and in the presence of ouabain 4.51 +/- 0.7 min. It is shown that the calculated Na+-transport pool is located in the cells. The Na+-transport pool under control conditions was 35.6 +/- 3.4 nmol/cm2, which corresponds to an intracellular Na+ concentration of 7.9 mM. Activation of the active Na+ transport by addition of antidiuretic hormone resulted in a highly significant increase in the Na+ transport pool, and inhibition of the transcellular Na+ transport with amiloride resulted in a decrease in the Na+-transport pool. Furthermore, the active Na+ transport increased along an S-shaped curve with increasing intracellular Na+ concentration (Na+-transport pool). The Na+ pump was found to be half saturated at an intracellular Na+ concentration of 12.5 mM.

Ionic and metabolic requirements for the hydroosmotic response to antidiuretic hormone in toad urinary bladder.

A study has been conducted to determine the ionic and metabolic requirements for full expression of the hydroosmotic response to antidiuretic hormone in the toad urinary bladder. By appropriate manipulation of incubation conditions it can be shown that there is a pool of serosal sodium necessary for a full hormone response. This serosal sodium pool is not related to the transepithelial sodium transport pool A full hydroosmotic response also requires serosal potassium; however, no specific anion requirement was demonstrated. Additionally, anaerobic or aerobic metabolism support a full hydroosmotic response equally well.

Interdependence of the two borders in a sodium transporting epithelium. Possible regulation by the transport pool

Specific binding of 14C-amiloride to the mucosal surface of frog skin epithelium (Rana temporaria) has been used as a measure of the number of sodium entry sites. All binding measurements were made with the mucosal surface bathed in a solution containing 1.1 mM sodium. When manipulations were used which increased the intracellular concentration of sodium the amount of amiloride bound was reduced. The manipulations included flushing the mucosal surface with solutions containing 111 mM sodium after serosal efflux was inhibited with ouabain or potassium removal. Similar results were obtained when cells were loaded with lithium. These effects on amiloride binding did not appear to depend on changes in membrane potential or upon changes in affinity of amiloride for its binding site. It appears that inhibition of serosal sodium efflux from the epithelium causes a reduction of mucosal sodium influx by making entry sites unavailable. This latter may be a result, directly or indirectly, of the sodium concentration in the sodium transport pool.

Epithelial cell electrolytes in relation to transepithelial sodium transport across toad urinary bladder.

Aspects of the relationships between cellular composition and transepithelial sodium transport across toad urinary bladder are reviewed. Changes in cellular sodium produced by amiloride, vasopressin, aldosterone, hypoxia, ouabain, and sodium-free media are consistent with a cellular sodium transport pool. Metabolic studies suggest that this pool gains its sodium from the mucosal medium and that there is little recycling of sodium between cell and serosal medium. One-third of the cellular potassium equilibrates readily with serosal potassium. The rate of exchange of potassium is much less than the rate of sodium transport supporting the contention that sodium transport in this tissue is electrogenic. Studies with 36Cl suggest that chloride does not cross the apical cellular membranes, but exchanges with serosal chloride. Possible relationships between transepithelial sodium transport and cellular volume regulation are discussed.

The sodium transport pool.

The sodium transport pool in epithelial cells represents sodium involved in active transport across the epithelium. There has been much controversy about the size of such a pool and even about its existence. Techniques for estimating the size of this pool are described. By analysis of toad bladder epithelial cells scraped from hemibladders mounted in chambers under a variety of conditions it has proved possible to detect and to quantify a sodium transport pool. Only about 20 percent of non-inulin space sodium measured flame photometrically is contained in this pool. This represents the total sodium entering cells from the mucosal medium, is in good agreement with the cellular sodium measured by the electron microprobe, and averages some 10-16 mmol/kg tissue H2O. Measurements of the pool in other tissues are considered.

Metabolic evidence that serosal sodium does not recycle through the active transepithelial transport pathway of toad bladder.

The possibility that sodium from the serosal bathing medium "back diffuses" into the active sodium transport pool within the mucosal epithelial cell of the isolated toad bladder was examined by determining the effect on the metabolism of the tissue of removing sodium from the serosal medium. It was expected that if recycling of serosal sodium did occur through the active transepithelial transport pathway of the isolated toad bladder, removal of sodium from the serosal medium would reduce the rate of CO2 production by the tissue and enhance of stoichiometric ratio of sodium ions transported across the bladder per molecula of sodium transport dependent CO2 produced simultaneously by the bladder (JNa/JCO2). The data revealed no significant change in this ratio (17.19 with serosal sodium and 16.13 after replacing serosal sodium with choline). Further, when transepithelial sodium transport was inhibited (a) by adding amiloride to the mucosal medium, or (b) by removing sodium from the mucosal medium, subsequent removal of sodium from the serosal medium, or (c) addition of ouabain failed to depress the basal rate of CO2 production by the bladder [(a)rate of basal, nontransport related, CO2 production (JbCO2) equals 1.54 +/- 0.52 with serosal sodium and 1.54 +/- 0.37 without serosal sodium; (b) Jb CO2 equals 2.18 +/- 0.21 with serosal sodium and 2.09 +/- 0.21 without serosal sodium; (c) 1.14 +/- 0.26 without ouabain and 1.13 +/- 0.25 with ouabain; unite of JbCO2 are nmoles mg d.w.-1 min-1]. The results support the hypothesis that little, if any, recycling of serosal sodium occurs in the total bladder.

The sodium transport pool in toad urinary bladder epithelial cells.

The sodium which equilibrates with 24-Na in epithelial cells of toad urinary bladders has been determined. With sodium Ringer's bathing both mucosal and serosal surfaces, 24-Na in the mucosal medium equilibrated with about 35 mmoles cellular sodium/kg cellular dry weight, representing about 20% of the total cellular sodium determined flame photometrically; 24-Na in the serosal medium equilibrated with 120 mmoles cellular sodium/kg cellular dry weight, about 80% of the total cellular sodium. With 24-Na in both media all cellular sodium was labeled within 30 min. In the absence of serosal sodium, total cellular sodium and that sodium which equilibrated with mucosal 24-Na in sodium Ringer's were both similar to the cellular sodium of mucosal origin which had been determined in epithelial cells exposed on both surfaces to sodium Ringer's. Sodium-free mucosal medium, and sodium Ringer's containing amiloride 10-4 or 10-3 M in the mucosal medium, both virtually completely inhibited transepithelial sodium transport. But, whereas the cellular sodium of mucosal origin fell to only 2 mmoles/kg cellular dry weight with sodium-free mucosal medium, an appreciable labeling of cellular sodium was found whether amiloride was present before, or only after, exposure of tissue to mucosal 24-Na. Rapid washing of the mucosal surface of hemibladders just before removal of epithelial cells for analysis removed most of this sodium labeled in the presence of amiloride, suggesting that the cellular sodium of mucosal origin consists of at least two fractions with only about two-thirds truly intracellular. The sodium transport pool measured directly in these experiments is appreciably smaller than any previous estimates of pool size all of which have been obtained by indirect techniques involving use of whole hemibladders rather than epithelial cells alone.

Effect of antidiuretic hormone on sodium uptake across outer surface of frog skin.

ARTICLESEffect of antidiuretic hormone on sodium uptake across outer surface of frog skinTU Biber, and LJ CruzTU Biber, and LJ CruzPublished Online:01 Oct 1973https://doi.org/10.1152/ajplegacy.1973.225.4.912MoreSectionsPDF (2 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation Cited ByRegulation of apical Na+ conductive transport in epithelia by pHBiochimica et Biophysica Acta (BBA) - Reviews on Biomembranes, Vol. 1241, No. 1NaCl Transport in Amphibian SkinThe role of sodium-channel density in the natriferic response of the toad urinary bladder to an antidiuretic hormoneThe Journal of Membrane Biology, Vol. 64, No. 1-2Effect of Li and of other ions on Na transport in epithelial cells of frog skinBiochemical Pharmacology, Vol. 29, No. 16Effect of external cation and anion substitutions on sodium transport in isolated frog skinThe Journal of Membrane Biology, Vol. 52, No. 2Effect of FeCl3 on ion transport in isolated frog skinThe Journal of Membrane Biology, Vol. 52, No. 2Colchicine inhibition of ADH effect on frog skin permeabilityExperientia, Vol. 34, No. 3Transport Across Amphibian SkinTransport Across Amphibian Urinary BladderIonic exchanges in isolated and open-circuited toad skinThe Journal of Membrane Biology, Vol. 35, No. 1Sodium pump stimulation by oxytocin and cyclic AMP in the isolated epithelium of the frog skinPflügers Archiv European Journal of Physiology, Vol. 371, No. 3Computer modelling. Application to studies on the initial rate of Na+ uptake by frog skin epidermisJournal of Theoretical Biology, Vol. 65, No. 4Effects of insulin on short-circuit current and Na-K-ATPase activity of the toad skin and urinary bladderComparative Biochemistry and Physiology Part A: Physiology, Vol. 58, No. 2Na-K-ATPase and transepithelial sodium transport in the toadComparative Biochemistry and Physiology Part A: Physiology, Vol. 56, No. 4Effects of Cd++ on short-circuit current across epithelial membranesThe Journal of Membrane Biology, Vol. 26, No. 1Solute transport across isolated epitheliaKidney International, Vol. 9, No. 2Structure and Function of the EpidermisLithium transport across isolated frog skin epitheliumThe Journal of Membrane Biology, Vol. 25, No. 1Effects of furosemide on sodium content and transport pool in frog skin (Rana esculenta)Naunyn-Schmiedeberg's Archives of Pharmacology, Vol. 290, No. 2-3 More from this issue > Volume 225Issue 4October 1973Pages 912-917 Copyright & PermissionsCopyright © 1973 by American Physiological Societyhttps://doi.org/10.1152/ajplegacy.1973.225.4.912PubMed4542709History Published online 1 October 1973 Published in print 1 October 1973 Metrics

The sodium transport pool in frog skin under open- and short-circuit conditions.

AbstractThe sodium pool of frog skin was studied by a method of continuous direct analysis under open‐ and short‐circuit conditions. No change in the transport pool on short‐circuiting was found. The results are discussed on the basis of proposed models for the sodium transport in frog skin.

Potassium dependence of base-line and ADH-stimulated sodium transport in toad bladder.

ARTICLESPotassium dependence of base-line and ADH-stimulated sodium transport in toad bladderSA MendozaSA MendozaPublished Online:01 Jul 1972https://doi.org/10.1152/ajplegacy.1972.223.1.120MoreSectionsPDF (1 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation Cited ByTransport Across Amphibian Urinary BladderRelationships between serosal medium potassium concentration and sodium transport in toad urinary bladderThe Journal of Membrane Biology, Vol. 26, No. 1Relationships between serosal medium potassium concentration and sodium transport in toad urinary bladderThe Journal of Membrane Biology, Vol. 26, No. 1Relationships between serosal medium potassium concentration and sodium transport in toad urinary bladderThe Journal of Membrane Biology, Vol. 26, No. 1A new model for regulation of sodium transport in high resistance epitheliaMedical Hypotheses, Vol. 2, No. 3The sodium transport pool in toad urinary bladder epithelial cellsThe Journal of Membrane Biology, Vol. 20, No. 1The kinetics of sodium transport in the toad urinary bladderThe Journal of Membrane Biology, Vol. 17, No. 1 More from this issue > Volume 223Issue 1July 1972Pages 120-124 Copyright & PermissionsCopyright © 1972 by American Physiological Societyhttps://doi.org/10.1152/ajplegacy.1972.223.1.120PubMed4339002History Published online 1 July 1972 Published in print 1 July 1972 Metrics

Effect of ADH, aldosterone, ouabain, and amiloride on toad bladder epithelial cells.

Effect of ADH, aldosterone, ouabain, and amiloride on toad bladder epithelial cells.

Effects of the diuretics, triamterene and mersalyl on active sodium transport mechanisms in isolated frog skin.

1. Triamterene reduces the rate coefficients for sodium movement into the transporting system of the isolated frog skin. The isotopically measured ;active sodium transport pool' is also reduced.2. Mersalyl reduces the rate coefficient for sodium and the calculated sodium flux from the transporting system to the inner bathing solution. The ;active sodium transport pool' is increased by this diuretic.3. The action of triamterene closely resembles that of amiloride and both reduce the entry of sodium into the system. In contrast, mersalyl limits the exit of sodium ions from the skin.

Changes in sodium pool and kinetics of sodium transport in frog skin produced by amiloride.

1. Amiloride produces a decrease in size of the active sodium transport pool of isolated frog skin.2. Rate coefficients for sodium movement into and out of the transporting cells across the outside membrane are decreased by amiloride. The rate coefficient for sodium extrusion across the inside membrane is not significantly affected.3. In the presence and in the absence of amiloride, the relation of sodium transport to outside sodium concentration exhibits similar saturation kinetics but amiloride reduces sodium transport rate at every sodium concentration of the outside solution.4. Labelling of skin with (14)C-amiloride from the outside solution is significantly greater than labelling with (14)C-inulin.5. The results of these studies suggest that amiloride reacts with sites on the outside membrane of the transporting cells as a result of which the rate of sodium movement across this membrane is diminished.

Compartmentation of the sodium transport pool of the toad bladder.

SummaryElution curves from both the mucosal and serosal sides of the toad bladder indicate that the sodium transport pool is not a single compartment as previously described in the literature. From 1 to 18 or more minutes there is evidence of two rates of elution from each side of the bladder. From 0 to 1 min there is evidence of a larger quantity of Na being eluted than can be expected from the ECF alone. Arguments are presented that there must be at least five compartments and perhaps as many as eight compartments in the sodium transport pool. Two of these compartments would be Na in the serosal and mucosal inulin spaces.The authors thank the following: Mr. W. E. Romans and Mr. Alan W. Selway of the medical school's Bioengineering Laboratory for their help in construction of the chambers; Dr. Frank T. Kallus for the design of the mucosal chamber; Mr. John Johnstone and Mrs. Lynn Peterson of the medical school's Scientific Computer Center for their assistance in treatment of the data and in programming t...