scholarly journals Amiloride sensitivity of the transepithelial electrical potential and of sodium and potassium transport in rat distal colon in vivo.

1981 ◽  
Vol 313 (1) ◽  
pp. 547-559 ◽  
Author(s):  
C J Edmonds
Keyword(s):  
Electrical Potential ◽  
Distal Colon ◽  
Potassium Transport ◽  
Rat Distal Colon ◽  
Sodium And Potassium

Evidence that aldosterone influences transport in target tissues by dissimilar mechanisms

1985 ◽  
Vol 248 (4) ◽  
pp. F507-F512 ◽  
Author(s):  
D. Hirsch ◽  
P. Pace ◽  
H. J. Binder ◽  
J. P. Hayslett
Keyword(s):  
Distal Colon ◽  
Proximal Colon ◽  
Potassium Transport ◽  
Potential Difference ◽  
Sodium Absorption ◽  
Potassium Secretion ◽  
Secondary Hyperaldosteronism ◽  
Induced Changes ◽  
Sodium And Potassium

The present study was performed to answer the question: Is the action of aldosterone on electrolyte transport and electrical properties similar in all target tissues? Studies were performed in vivo in control animals and rats with secondary hyperaldosteronism, caused by a sodium-free diet, to compare the effects of hyperaldosteronism on distal colon with hormone-induced changes in proximal colon. In distal colon aldosterone increased net sodium absorption and potassium secretion approximately threefold. Transmural potential difference increased from -15 +/- 2 to -83 +/- 3 mV (lumen negative) and ISC rose from 167 +/- 26 to 1,023 +/- 17 microA X cm-2. These aldosterone-induced responses were completely inhibited by 0.1 mM amiloride. In contrast, in proximal colon potential difference was unchanged or increased slightly in experimental animals and ISC increased only 28% above control, although increases in net sodium and potassium transport were similar to changes observed in distal colon. Amiloride did not reduce sodium absorption in proximal colon of animals with hyperaldosteronism; ISC was decreased by 43%. These studies demonstrate that rat proximal colon is an aldosterone-sensitive tissue, but that the mechanism by which aldosterone influences sodium transport is not identical in distal and proximal portions of colon.

Bicarbonate secretion modulates ammonium absorption in rat distal colon in vivo

1988 ◽  
Vol 254 (5) ◽  
pp. F657-F667 ◽  
Author(s):  
R. M. Cohen ◽  
R. L. Stephenson ◽  
G. M. Feldman
Keyword(s):  
Carbon Dioxide ◽  
Kinetic Studies ◽  
Distal Colon ◽  
Bicarbonate Secretion ◽  
Fixed Rate ◽  
Parallel Change ◽  
Rat Distal Colon ◽  
Total Ammonia ◽  
Ammonia Absorption

Although the mammalian colon is thought to absorb large quantities of total ammonia, principally in the form of NH3, quantitative support for this hypothesis is lacking. In rat distal colon, we observed that NH3 was approximately 400 times more permeant than NH+4. In addition, colonic HCO-3 secretion influenced total ammonia (NH3 plus NH+4) absorption; that is, alteration of HCO-3 secretion caused a parallel change in total ammonia absorption. Perfusion with total ammonia also caused net HCO-3 secretion to switch to net absorption, and, in the setting of preexisting HCO-3 absorption, perfusate containing total ammonia enhanced HCO-3 absorption. These events suggest that colonic HCO-3 secretion titrates luminal NH+4 to NH3, permitting NH3 to diffuse from the lumen, while HCO-3 is titrated to carbon dioxide and also diffuses from the lumen. In support of titration of NH+4 and HCO-3, the magnitude of induced HCO-3 absorption approximated total ammonia absorption. This titration relationship suggests that, in kinetic studies, total ammonia absorption will be limited by a fixed rate of HCO-3 secretion. A model was developed that simulated these events.

scholarly journals The Serum- and Glucocorticoid-Induced Kinase Is a Physiological Mediator of Aldosterone Action*

Endocrinology ◽  
2001 ◽  
Vol 142 (4) ◽  
pp. 1587-1594 ◽  
Author(s):  
Aditi Bhargava ◽  
Meryl J. Fullerton ◽  
Kathy Myles ◽  
Timothy M. Purdy ◽  
John W. Funder ◽  
...  
Keyword(s):  
In Situ Hybridization ◽  
Messenger Rna ◽  
Time Course ◽  
Rat Kidney ◽  
Distal Colon ◽  
Mrna Levels ◽  
Epithelial Tissues ◽  
Sodium And Potassium

Abstract Aldosterone plays a major role in regulating sodium and potassium flux in epithelial tissues such as kidney and colon. Recent evidence suggests that serum- and glucocorticoid-regulated kinase (SGK) is induced by aldosterone and acts as a key mediator of aldosterone action in epithelial tissues. Induction of SGK messenger RNA (mRNA) has previously been shown within 30 min of addition of supraphysiological doses of aldosterone to Xenopus A6 cells and within 4 h in rat kidney in vivo. In this study we determined the time course of SGK induction, at doses of aldosterone in the physiological range, in rat kidney and colon, using Northern and Western blot analyses and in situ hybridization and determined concurrent changes in urinary sodium and potassium excretion by Kagawa bioassay. On Northern blot analysis, SGK mRNA levels were significantly elevated in both kidney and colon 60 min after the injection of aldosterone. SGK protein in late distal colon was significantly elevated 2 and 4 h after aldosterone treatment. In situ hybridization showed SGK mRNA to be induced in renal collecting ducts and distal tubular elements in both cortex and medulla by doses of aldosterone of 0.1 μg/100 g BW or more within 30 min of steroid treatment. Significant changes in urinary composition were similarly seen with an aldosterone dose of 0.1 μg/100 g BW from 90 min after aldosterone injection. The early onset of SGK induction in kidney and colon and the correlation with urinary changes in terms of both time course and dose response suggest that SGK plays an important role in mediating the effects of aldosterone on sodium homeostasis in vivo.

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

1990 ◽  
Vol 124 (1) ◽  
pp. 47-52 ◽  
Author(s):  
C. J. Edmonds ◽  
C. L. Willis
Keyword(s):  
Electrical Potential ◽  
Dry Weight ◽  
Potassium Transport ◽  
Plasma Sodium ◽  
Electrical Potential Difference ◽  
Stimulant Effect ◽  
Potassium Adaptation ◽  
Short Period ◽  
Potassium Secretion ◽  
Sodium And Potassium

ABSTRACT 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<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. Journal of Endocrinology (1990) 124, 47–52

Modified Absorptive and Secretory Processes in the Rat Distal Colon after Neutron Irradiation: In Vivo and In Vitro Studies

1999 ◽  
Vol 151 (4) ◽  
pp. 468 ◽  
Author(s):  
Agnès François ◽  
Isabelle Dublineau ◽  
Fabienne Lebrun ◽  
Brigitte Ksas ◽  
Nina M. Griffiths ◽  
...  
Keyword(s):  
Neutron Irradiation ◽  
Distal Colon ◽  
In Vitro Studies ◽  
Rat Distal Colon

Ontogeny of K+ transport in rat distal colon

1996 ◽  
Vol 271 (2) ◽  
pp. G268-G274 ◽  
Author(s):  
R. I. Aizman ◽  
G. Celsi ◽  
L. Grahnquist ◽  
Z. M. Wang ◽  
Y. Finkel ◽  
...  
Keyword(s):  
Atp Hydrolysis ◽  
Apical Membrane ◽  
Distal Colon ◽  
Relative Activity ◽  
K Uptake ◽  
Perfusion Studies ◽  
Rat Distal Colon ◽  
P Type ◽  
K Transport

Infants need to retain more K+ than adults to avoid growth retardation. Since the K+ requirements are different in infants (I) and in adults (A), the mechanisms regulating K+ homeostasis should also be different. The colon plays an important role for the regulation of K+ homeostasis. Colonic K+ transport is bidirectional. In this study we have examined the development of colonic K+ transport with special reference to the contribution of different K(+)-transporting pathways. The net colonic K+ uptake, as determined by in vivo perfusion studies and by 86Rb uptake, was significantly higher in I than in A rats. In both I and A colon, approximately 80% of total 86Rb uptake was dependent on vanadate-sensitive P-type adenosinetriphosphatases (ATPases), but the contribution of these different ATPases changes during development. The activity of colonic Na(+)-K(+)-ATPase, measured as ouabain-sensitive Na(+)-dependent ATP hydrolysis and as 86Rb uptake, was lower in I than in A rats. In contrast, the activity of K(+)-ATPases located in apical membrane and measured as ouabain insensitive and SCH-28080 sensitive, as ouabain-sensitive Na(+)-independent ATP hydrolysis, and as 86Rb uptake was significantly higher in I than in A rats. The ratio between apically located K(+)-ATPases and basolateral Na(+)-K(+)-ATPase activities was almost 3.2-fold higher in I than in A colon. We identified with Northern blot the expression of the colonic H(+)-K(+)-ATPase and the Na(+)-K(+)-ATPase alpha-subunits. The alpha-mRNA expression of both ATPases was significantly higher in I than in A rats. The pH and K+ sensitivity of the ouabain-insensitive, SCH-28080-sensitive K(+)-ATPase was the same in I and A colons. In conclusion, the relative activity of apical K+ absorbing ATPases is higher in the I than in the A colon, which should aid infants in retaining K+.

Control of potassium transport by turtle colon: role of membrane potential

1984 ◽  
Vol 247 (1) ◽  
pp. C26-C32 ◽  
Author(s):  
D. R. Halm ◽  
D. C. Dawson
Keyword(s):  
Electrical Potential ◽  
Potassium Transport ◽  
Sodium Absorption ◽  
Electrical Potential Difference ◽  
Sodium Potassium ◽  
Pump Rate ◽  
Potassium Secretion ◽  
Sodium Potassium Pump

To more clearly define the role of the transepithelial electrical potential difference (V m----s), potassium permeability, and sodium-potassium pump rate in transcellular potassium transport by isolated turtle colon, we measured transmural potassium fluxes under open-circuit conditions in the presence and absence of putative blockers of potassium transport: amiloride and barium. The results were consistent with the notion that V m----s is a major determinant of cellular potassium secretion, whereas active potassium absorption is insensitive to changes in V m----s. These observations suggest that “coupling” between colonic sodium absorption and potassium secretion in vivo could be due primarily to the effect of the lumen negative V m----s on transcellular secretory potassium flow. Amiloride-induced inhibition of potassium secretion appeared to be due to the reductions in V m----s and sodium-potassium pump rate that accompanied the inhibition of active sodium absorption.

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