scholarly journals The Coupling of the Short-Circuit Current to Metabolism in the Urinary Bladder of the Toad

1963 ◽  
Vol 46 (4) ◽  
pp. 733-754 ◽  
Author(s):  
Roy H. Maffly ◽  
I. S. Edelman
Keyword(s):  
Tricarboxylic Acid Cycle ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Metabolic Effects ◽  
Metabolic Inhibitors ◽  
Na Transport ◽  
Bathing Medium ◽  
Free Media ◽  
Tricarboxylic Acid Cycle Intermediates

The relationship of the short-circuit current to metabolism was studied in the toad bladder in vitro. Substrates and inhibitors were added to the bathing medium and the effect on the short-circuit current was determined. The spontaneous decline in the short-circuit current that occurred in substrate-free media was prevented or reversed by the addition of glucose, pyruvate, lactate, or ß-hydroxybutyrate, whereas acetate and tricarboxylic acid cycle intermediates had no effect. A variety of metabolic inhibitors depressed the short-circuit current; depression by iodoacetate and by malonate was delayed by prior addition of pyruvate or lactate but not by glucose. The ability of a substrate to stimulate the current did not correlate with its rate of oxidation to CO2. On the basis of earlier studies, the metabolic effects on the short-circuit current were assumed to reflect equivalent effects on the rate of active Na transport. It is suggested that the energy for Na transport is provided not by a general cellular metabolic pool but by a specific metabolic pathway or pathways spatially linked to the transport mechanism.

Association between HCO3(-) absorption and K+ uptake by Amphiuma jejunum: relations among HCO3(-) absorption, luminal K+, and intracellular K+ activity

1984 ◽  
Vol 246 (6) ◽  
pp. G732-G744
Author(s):  
M. A. Imon ◽  
J. F. White
Keyword(s):  
Short Circuit ◽  
Short Circuit Current ◽  
Uptake Mechanism ◽  
Bathing Medium ◽  
The Media ◽  
Absorptive Flux ◽  
Free Media ◽  
Intracellular K Activity ◽  
K Activity

Titration techniques and K+- sensitive microelectrodes have been used to investigate the relations among HCO3(-) absorption, luminal K+, and intracellular K+ activity in in vitro Amphiuma jejunum. The HCO3(-) absorptive flux (JHCO3(-] measured by pH-stat under short circuit was reduced by removal of K+ from the medium but not by replacement of Na+ with choline. JHCO3(-) exhibited a seasonal variation when K+ was absent from the media and was increased to a maximum when K+ equaled 5 mM. Addition of K+ to a K+-free luminal medium stimulated JHCO3(-) much more than addition to the serosal medium. Acetazolamide (10(-4) M) blocked K+-stimulated HCO3(-) absorption while benzolamide reduced the short-circuit current associated with HCO3(-) absorption much more rapidly when added to the mucosal bathing medium. Intracellular K+ activity (aik) and mucosal membrane potential (psi m) of jejunal villus cells were measured with double-barreled microelectrodes. When bathed bilaterally with HCO3(-)-containing media, K+ was actively accumulated for many hours (aik = 58.5 mM) but in the presence of ouabain fell to equilibrium (16 mM) after 2 h. In contrast, when HCO3(-) absorption was induced by removal of serosal HCO3(-), aik was elevated to 83.6 mM and, after 4-h exposure to ouabain cell K+, remained far above electrochemical equilibrium at 33 mM. Tissues bathed in Na+-free (Tris) media containing ouabain retained cell K+ after 4 h at even higher levels (46 mM). Cell K+ activity was reduced by removal of K+ from either the mucosal or serosal medium. Acetazolamide reduced aik over 2 h in Na+-free media from 66 to 42 mM. The decline in aik was associated with a concomitant decline in the HCO3(-) absorptive current. It is concluded that K+ is actively accumulated across both luminal and serosal membranes of the jejunal absorptive cell and that the luminal uptake mechanism is linked to HCO3(-) absorption or an equivalent process.

Ion transport by amphibian antrum in vitro. I. General characteristics

1975 ◽  
Vol 228 (4) ◽  
pp. 1188-1198 ◽  
Author(s):  
G Flemstrom ◽  
TG Sachs
Keyword(s):  
Secretory Cell ◽  
Short Circuit ◽  
Ussing Chamber ◽  
Short Circuit Current ◽  
Metabolic Inhibitors ◽  
Na Transport ◽  
Alkaline Secretion ◽  
Chamber Measurements ◽  
Net Fluxes

Both Necturus and bullfrog antrum show stable PD, resistance, and short-circuit current (Isc) when mounted in an Ussing chamber. Measurements of Na+ and Cl minus flux showed that both ions are actively transported across Necturus antrum, Na+ from secretory to nutrient, Cl minus from nutrient to secretory (both net fluxes being similar to 0.30 mueq cm minus 2 h minus 1). Only the Na+ transport contributed to the Isc and PD as evidenced by a) Na+ removal, b) the effects of amiloride on the secretory surface, c) the effects of ouabain on the nutrient side. Microelectrode experiments confirm the Na+ conductance of the secretory cell membrance, a HCO3 minus conductance of both cell membranes, and a KCl conductance across the nutrient cell membrane. In addition, antrum apparently secretes alkali (similar to 0.35 mueq cm minus 2 h minus 1), which secretion is sensitive to metabolic inhibitors and Diamox. Nutrientside HCO3 minus increased the rate of alkaline secretion and a transmucosal HCO3 minus gradient could contribute to ISC and PD. A model is proposed to account for the electrical properties of the tissue.

THE EFFECT OF VALINOMYCIN ON THE TOAD BLADDER: ANTAGONISM TO VASOPRESSIN AND ALDOSTERONE

1969 ◽  
Vol 45 (2) ◽  
pp. 287-295 ◽  
Author(s):  
P. J. BENTLEY
Keyword(s):  
Macrolide Antibiotic ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Water Transfer ◽  
Toad Bladder ◽  
Na Transport ◽  
Bathing Medium ◽  
Sodium Transfer ◽  
Sites Of Action ◽  
Subsequent Addition

SUMMARY The macrolide antibiotic valinomycin decreased short-circuit current (SCC, Na transport) across the isolated bladder of the toad. This effect was not overcome by increasing the K+ levels in the bathing medium or by the action of amphotericin B. The effects of vasopressin on both sodium and water transfer across the toad bladder were inhibited by valinomycin and the latter inhibition is non-competitive. The action of theophylline in increasing water transfer across the bladder was also inhibited. Cyclic AMP also increased water and Na+ transfer across the bladder but its action was not reduced by the macrolide. These results suggest that valinomycin inhibits adenyl cyclase. Aldosterone increases sodium transport across the toad bladder and this action was abolished by previous incubation of the tissue with the macrolide. Once the steroid-induced effect had been established subsequent addition of valinomycin did not alter the sodium transfer. Valinomycin thus appears to have several sites of action on the toad bladder.

Steroid hormone stimulation of Na+ transport in A6 cells is mediated via glucocorticoid receptors

1993 ◽  
Vol 264 (4) ◽  
pp. C875-C884 ◽  
Author(s):  
T. J. Schmidt ◽  
R. F. Husted ◽  
J. B. Stokes
Keyword(s):  
Cell Line ◽  
Glucocorticoid Receptors ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Mineralocorticoid Receptors ◽  
Na Transport ◽  
Receptor Complexes ◽  
Binding Forms ◽  
Mineralocorticoid Antagonists

The A6 cell line derived from the toad kidney forms polarized, highly differentiated epithelial monolayers in culture and has been utilized as an experimental model for studying regulation of transepithelial Na+ transport by aldosterone. In the present study we evaluated the specific role(s) of glucocorticoid and mineralocorticoid receptors in mediating this enhanced electrogenic Na+ transport, which was measured experimentally as an increase in short-circuit current (Isc). Our data demonstrate that specific glucocorticoid agonists (100 nM), including RU 28362 and RU 26988, elicit “mineralocorticoid-like” increases in Isc that are blocked by the glucocorticoid antagonist RU 38486 but are unaffected by mineralocorticoid antagonists including RU 28318 and RU 26752. The stimulatory effects of aldosterone (100 nM) were also blocked by RU 38486 and not by mineralocorticoid antagonists. These data extend earlier studies suggesting that in this cell line aldosterone mediates its physiological effects via binding with relatively low affinity (dissociation constant Kd congruent to 25-50 nM) to glucocorticoid receptors, despite the presence of apparently normal mineralocorticoid receptors. Our in vitro biochemical studies also demonstrate that A6 glucocorticoid receptor complexes can be thermally activated or transformed to DNA binding forms which exhibitaltered elution profiles from anion-exchange resins. Thus, based on several criteria, these amphibian glucocorticoid receptors appear very similar to classical mammalian receptors and are capable of mediating all of the stimulatory effects of aldosterone on net Na+ transport.

Avian cecum: role of glucose and volatile fatty acids in transepithelial ion transport

1991 ◽  
Vol 260 (5) ◽  
pp. G703-G710 ◽  
Author(s):  
B. R. Grubb
Keyword(s):  
Fatty Acids ◽  
Ion Transport ◽  
Volatile Fatty Acids ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Serosal Side ◽  
Na Transport ◽  
Cl Secretion ◽  
Mucosal Side

In the fowl cecum in vitro, the influence of glucose and the three most prevalent naturally occurring volatile fatty acids (acetate, propionate, butyrate) on short-circuit current (Isc), electrical resistance, and transport of Na and Cl was determined. When glucose, acetate, or butyrate was present, ion transport was characterized by electrogenic Na absorption, greater than 65% of which was amiloride inhibitable, and Cl secretion, which also was electrogenic. Isc could be completely accounted for by net fluxes of Na and Cl. When glucose, acetate, or butyrate (10 mM both sides) was included in the incubation medium, cecal tissue maintained its Isc and a constant rate of net Na absorption and Cl secretion for a 5-h period. When no substrate was present or propionate was included in the medium, a marked fall in Isc and net Na and Cl fluxes was seen. Glucose caused an increase in Isc when added only to the serosal side. As 3-O-methylglucose (not metabolized) was not effective in stimulating Isc of the cecum (serosal or mucosal addition), it appeared that glucose increased Isc by acting as an energy substrate for active Na transport. Acetate and butyrate appeared to be equally effective in stimulating Na transport and Isc when placed on either side of the membrane. When the preparation was supplied with glucose (serosal side) and acetate was added to the mucosal side, no further stimulation of Isc occurred. Thus it appeared that acetate and butyrate were acting as substrates for active Na transport rather than stimulating Na transport by some other mechanism such as a cotransport with Na.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective effects of bumetanide on chloride transport in bullfrog cornea

1978 ◽  
Vol 234 (4) ◽  
pp. F297-F301
Author(s):  
O. A. Candia ◽  
H. F. Schoen
Keyword(s):  
Electrical Resistance ◽  
Loop Diuretic ◽  
Chloride Transport ◽  
Short Circuit ◽  
Ussing Chamber ◽  
Short Circuit Current ◽  
Selective Inhibitor ◽  
O2 Consumption ◽  
Na Transport ◽  
Bathing Medium

Frog corneas were mounted in a modified Ussing chamber and short-circuit current (SCC) and unidirectional Cl fluxes were measured. Bumetanide, a loop diuretic, at concentrations as low as 10(-7) M, reduced the SCC 29%. At 10(-5) M, bumetanide reduced the SCC 96% and increased transcorneal electrical resistance 20-51%. The forward Cl flux declined from 0.71 +/- 0.04 to 0.20 +/- 0.03 mueq/h.cm2 (n, 7), while, in separate experiments, the backward Cl flux did not change significantly (from 0.22 +/- 0.03 to 0.23 +/- 0.04; n, 7). When corneas were mounted in Cl-free Ringer and the net Na transport was stimulated with amphotericin B, 10(-5) M bumetanide had no effect on the SCC. In separate experiments the effect of 10(-5) M bumetanide on the O2 consumption was measured in a stirrer bath assembly. Bumetanide decreased the O2 consumption from 352 +/- 14 to 297 +/- 19 microliter/h.cm2 (significantly different from sham-treated controls). This decrease was similar to that obtained with furosemide or when Cl was removed from the bathing medium. We infer from these results that bumetanide is a selective inhibitor of active Cl transport in the bullfrog cornea.

In vitro studies of sodium transport across the lower intestine of a desert parrot

1980 ◽  
Vol 239 (3) ◽  
pp. R285-R290
Author(s):  
E. Skadhauge ◽  
T. J. Dawson
Keyword(s):  
Short Circuit ◽  
Electrical Potential ◽  
Flux Ratio ◽  
Short Circuit Current ◽  
Electrical Potential Difference ◽  
Na Transport ◽  
Salt Loading ◽  
Ussing Chambers ◽  
Lower Intestine

The lower intestine (coprodeum and colon) of the Australian parrot, the galah, was mounted in Ussing chambers. Short-circuit current (SCC), electrical potential difference (PD), and unidirectional fluxes of Na and Cl were measured in birds that were fed mixed seeds or were NaCl loaded. The net Na transport of both coprodeum and colon was nearly equal to the SCC, and the flux ratio for Cl was unity. In birds which received mixed seeds, average coprodeal Na transport was 7.8 mu eq . cm-2 . h-1, and PD was 19 mV. The Km for Na was 5.7 meq/l. In colon, Na transport was reduced by 67% and PD by 70%. The ratio between unidirectional Na and Cl fluxes in the serosa-mucosa direction was 0.7. Salt loading suppressed coprodeal, but increased colonic Na transport. The coprodeal and colonic SCC and NA transport of birds receiving mixed seeds were inhibited by amiloride on the mucosal side. Colonic SCC of NaCl-loaded birds was only slightly reduced by amiloride (by 17%), but stimulated by amino acids (by 18%).

Chronic regulation of transepithelial Na+ transport by the rate of apical Na+ entry

1996 ◽  
Vol 270 (2) ◽  
pp. C600-C607 ◽  
Author(s):  
M. D. Rokaw ◽  
E. Sarac ◽  
E. Lechman ◽  
M. West ◽  
J. Angeski ◽  
...  
Keyword(s):  
Short Circuit ◽  
Basolateral Membrane ◽  
Short Circuit Current ◽  
Maximal Activity ◽  
Na Channels ◽  
Na Transport ◽  
Bottom Structures ◽  
Stimulation Of

In several settings in vivo, prolonged inhibition of apical Na+ entry reduces and prolonged stimulation of apical entry enhances the ability of renal epithelial cells to reabsorb Na+, an important feature of the load-dependent regulation of renal tubular Na+ transport. To model this load dependency, apical Na+ entry was inhibited or stimulated for 18 h in A6 cells and vectorial transport was measured as short-circuit current (Isc) across monolayers on filter-bottom structures. Basal amiloride-sensitive Isc represents the activity of apical Na+ channels, whereas Isc after permeabilization of the apical membrane to cations with nystatin represents maximal activity of the basolateral Na(+)-K(+)-ATPase. Chronic inhibition of apical Na+ entry by 18-h apical exposure to amiloride or replacement of apical Na+ with tetramethylammonium (TMA+), followed by washing and restoration of normal apical medium, revealed a persistent decrease in Isc that remained despite exposure to nystatin. Both basal and nystatin-stimulated Isc recovered progressively after restoration of normal apical medium. In contrast, chronic stimulation of apical Na+ entry by short circuiting the epithelium increased Isc in the absence and presence of nystatin, indicating upregulation of both apical Na+ channels and basolateral Na(+)-K(+)-ATPase. Basolateral equilibrium [3H]ouabain binding was reduced to 67 +/- 5% in TMA+ vs. control cells, whereas values in 18-h short-circuited cells increased by 42 +/- 19%. The results demonstrate that load dependency of tubular Na+ transport can be modeled in vitro and indicate that the regulation of Na(+)-K(+)-ATPase observed in these studies occurs in part by changes in the density of functional transporter proteins within the basolateral membrane.

Effect of sulfidopeptide leukotrienes D4 and E4 on ileal ion transport in vitro in the rat and rabbit

1988 ◽  
Vol 255 (2) ◽  
pp. G175-G183 ◽  
Author(s):  
P. L. Smith ◽  
D. P. Montzka ◽  
G. P. McCafferty ◽  
M. A. Wasserman ◽  
J. D. Fondacaro
Keyword(s):  
Short Circuit ◽  
Short Circuit Current ◽  
Bathing Solution ◽  
Na Transport ◽  
Rabbit Ileum ◽  
Rat Ileum ◽  
Ussing Chambers ◽  
Meclofenamic Acid ◽  
Acid Metabolites

Effects of leukotrienes D4 and E4 (LTD4 and LTE4) on electrolyte transport were examined, employing stripped segments of rat and rabbit ileum mounted in Ussing chambers. Addition of LTD4 or LTE4 to the serosal but not the mucosal bathing solution elicited a transient increase in short-circuit current (Isc) with maximal responses seen at 10(-5) M and 10(-8) M in rat and rabbit respectively and a sustained decrease in transepithelial conductance (Gt) in the rat only. In the rat, Cl replacement, reduction of bathing solution [Ca2+] to 1 microM or pretreatment with 1 microM indomethacin or meclofenamic acid inhibited the LTD4- or LTE4-induced Isc changes with no effect on the decrease in Gt. LTD4 (10 microM) transiently increased net Cl secretion and produced a sustained decrease in both unidirectional and net Na transport and mucosal-to-serosal Cl flux in rat ileum. The decrease in unidirectional Na fluxes is accounted for predominantly by a change in the potential independent flux of Na. These results suggest that the increase in Isc in both rat and rabbit is mediated by arachidonic acid metabolites, whereas the decrease in Gt and net Na absorption in rat ileum is mediated by a cyclooxygenase-independent pathway.

Suppression of coupled Na-Cl absorption by aldosterone and dexamethasone in rat distal colon in vitro

1984 ◽  
Vol 246 (6) ◽  
pp. F785-F793 ◽  
Author(s):  
R. D. Perrone ◽  
S. L. Jenks
Keyword(s):  
Short Circuit ◽  
Short Circuit Current ◽  
Distal Colon ◽  
Rat Colon ◽  
Na Transport ◽  
Unidirectional Flux ◽  
Rat Distal Colon ◽  
Marked Suppression ◽  
Stimulation Of

Basal Na absorption in the rat colon is coupled to that of Cl in an electroneutral fashion. We previously determined that aldosterone or dexamethasone induces amiloride-sensitive mucosal-to-serosal Na flux approximately equal to the amiloride-sensitive short-circuit current in rat distal colon in vitro. However, the effect of these steroids on coupled Na-Cl absorption was not examined. For this purpose, we determined the unidirectional flux of Na and Cl in voltage-clamped distal colon segments from rats treated with aldosterone or dexamethasone. Amiloride was used as a probe for conductive Na absorption, and acetazolamide and Cl-free solutions were used as probes for coupled Na-Cl absorption. Our results indicate that the nature of colonic Na absorption is markedly changed after treatment with these steroids. In contrast to findings in the untreated rat, colonic Na absorption after treatment with aldosterone or dexamethasone was largely independent of the presence of Cl. Net Cl absorption and acetazolamide sensitivity were both greatly diminished. Thus, aldosterone and dexamethasone have multiple effects on Na transport in rat distal colon. In addition to the stimulation of conductive Na absorption by aldosterone, an effect well described in other epithelia, there is marked suppression of coupled Na-Cl absorption. Dexamethasone was less effective in suppressing Cl absorption but equally effective in stimulating conductive Na absorption. These steroid effects were greater in the terminal 1-2 cm of the rat colon.

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