NaCl-dependent expression of amiloride-blockable Na+ channel in Xenopus oocytes

Asher, Carol; Singer, Donald H.; Eren, Rachel; Yeger, Orna; Dascal, Nathan; Garty, Haim

doi:10.1152/ajpgi.1992.262.2.g244

Cited by 9 publications

(6 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, earlier studies in A6 cells showed that aldosterone increases Na ϩ entry at the apical membrane by changing the activity of channels that are already present in the apical membrane and not by increasing the number of channels (13). Although interpretation of other electrophysiological data remains controversial (14 -16), biochemical methods support the original observation that ENaC mRNA and ENaC protein in the apical membrane does not increase in the presence of aldosterone (at least in the first 2-4 h when the increase in sodium transport is most dramatic) (10,(17)(18)(19).Since the action of aldosterone appears to involve a mechanism that increases the P o of sodium channels, an examination of post-translational mechanisms that alter P o may offer some insight into the mechanism of aldosterone action, but identifying signal transduction pathways that can increase sodium channel P o in A6 cells has been difficult. There have been many suggestions about potential aldosterone-induced post-translational modifications, but in the context of our previous results (20 -22), one is particularly interesting.…”

mentioning

confidence: 80%

mentioning

confidence: 89%

See 1 more Smart Citation

Methylation Increases the Open Probability of the Epithelial Sodium Channel in A6 Epithelia

Becchetti¹,

Kemendy²,

Stockand³

et al. 2000

Journal of Biological Chemistry

View full text Add to dashboard Cite

We used single channel methods on A6 renal cells to study the regulation by methylation reactions of epithelial sodium channels. 3-Deazaadenosine (3-DZA), a methyltransferase blocker, produced a 5-fold decrease in sodium transport and a 6-fold decrease in apical sodium channel activity by decreasing channel open probability (P o ). 3-Deazaadenosine also blocked the increase in channel open probability associated with addition of aldosterone. Sodium channel activity in excised "insideout" patches usually decreased within 1-2 min; in the presence of S-adenosyl-L-methionine (AdoMet), activity persisted for 5-8 min. Sodium channel mean time open (t open ) before and after patch excision was higher in the presence of AdoMet than in untreated excised patches but less than t open in cell-attached patches. Sodium channel activity in excised patches exposed to both AdoMet and GTP usually remained stable for more than 10 min, and P o and the number of active channels per patch were close to values in cell-attached patches from untreated cells. These findings suggest that a methylation reaction contributes to the activity of epithelial sodium channels in A6 cells and is directed to some regulatory element closely connected with the channel, whose activity also depends on the presence of intracellular GTP.The amiloride-blockable, highly selective, epithelial sodium channel (ENaC) 1 present on the apical surface of principal cells in mammalian renal cortical collecting tubules is the primary site for the regulation of total body sodium balance and blood pressure. The cell line, A6, derived from distal tubules of Xenopus laevis nephrons, is a good experimental model for the study of these sodium channels. When grown on permeable supports in the presence of aldosterone, A6 cells express an apical sodium channel with properties identical to those of channels in mammalian tissues (1).Despite many studies, the mechanism by which aldosterone stimulates apical sodium transport is still poorly understood. It is known that the complex between aldosterone and its intracellular receptor activates gene expression and induces the synthesis of proteins (2-9); however, little is known about the cellular functions of the induced proteins except that the final result is an increase in sodium transport (2, 9 -11). Originally, because of the observation that protein synthesis was required for aldosterone to increase sodium transport, it was postulated that aldosterone induced sodium channel synthesis and insertion. However, earlier studies in A6 cells showed that aldosterone increases Na ϩ entry at the apical membrane by changing the activity of channels that are already present in the apical membrane and not by increasing the number of channels (13). Although interpretation of other electrophysiological data remains controversial (14 -16), biochemical methods support the original observation that ENaC mRNA and ENaC protein in the apical membrane does not increase in the presence of aldosterone (at least in the first 2-4 h when the increase ...

show abstract

mentioning

confidence: 80%

mentioning

confidence: 89%

Methylation Increases the Open Probability of the Epithelial Sodium Channel in A6 Epithelia

Becchetti¹,

Kemendy²,

Stockand³

et al. 2000

Journal of Biological Chemistry

View full text Add to dashboard Cite

show abstract

“…By contrast, distal Na + -H + :Cl --HCO 3 -dual exchange is suppressed completely, and replaced by an electrogenic Na + -absorptive process which involves the appearance of ENaC in the apical membrane of surface colonocytes [12,20,25]. This response to aldosterone is not peculiar to rat distal colon, as similar enhancements of electrogenic Na + transport and apical ENaC expression occur in the distal colon or equivalent intestinal segment in humans, pig and chicken [1,11,31]. Although a recent study has compared the effect of dietary Na + depletion on ENaC subunit mRNA expression in the proximal and distal segments of rat colon [37], this was not correlated with changes in the expression of ENaC subunit proteins.…”

Section: Introductionmentioning

confidence: 99%

Segmental variability of ENaC subunit expression in rat colon during dietary sodium depletion

Baker

Mathialahan

et al. 2002

Pfl�gers Archiv European Journal of Physiology

View full text Add to dashboard Cite

In rat distal colon, aldosterone has little effect on Na(+) channel (ENaC) alpha-subunit levels but increases the expression of the beta- and gamma-subunits and stimulates electrogenic Na(+) transport. By contrast, the molecular basis of aldosterone's inability to stimulate electrogenic Na(+) transport in the proximal colon is unclear. We therefore compared the effects of hyperaldosteronism secondary to 10 days dietary Na(+) depletion on ENaC subunit expression in rat proximal and distal colon. Northern analyses revealed appreciable and similar levels of alpha-subunit mRNA throughout the colon in control and Na(+)-depleted animals. By contrast, Na(+) depletion substantially enhanced beta-subunit mRNA expression in the distal colon, but had no effect on the low expression levels of beta-subunit mRNA in the proximal colon. Expression of the gamma-subunit, evaluated by PCR, was also restricted to the distal colon of Na(+)-depleted animals. Western analyses demonstrated similar levels of alpha-subunit protein in the proximal and distal colon of both groups of animals, whereas beta-subunit and gamma-subunit proteins were detected solely or predominantly in the distal colon of the Na(+)-depleted animals. Immunocytochemistry confirmed that significant levels of all three subunit proteins only occurred in the apical membrane of surface cells in the distal colon of Na(+)-depleted animals. Our findings are consistent with previous studies demonstrating that aldosterone stimulates electrogenic Na(+) transport in rat distal colon by increasing the expression of beta- and gamma-subunit mRNA and protein, and thus the amount of functional heteromeric ENaC protein in the apical domain. They also show that aldosterone is incapable of stimulating electrogenic Na(+) transport in rat proximal colon (despite the presence of alpha-subunit mRNA and protein) because of its inability to enhance beta- and gamma-subunit expression in this segment.

show abstract

“…However, a puzzling aspect of this system is the repeated observation that low-salt (LS) diets reduce or even eliminate the colonic sodium-linked cotransporter activities, while concurrently inducing the expression of electrogenic amiloride-sensitive sodium channels (ENaCs) (3,10,27,34). The upregulation of ENaC activity is also seen in coprodeum (the more distal segment of the avian lower intestine), and it resembles the aldosterone-mediated regulation of ENaCs in mammalian colon and other target tissues (4,9,15,16,(33)(34)(35). When hens are acutely resalinated or adapted to high-salt (HS) diets, the colonic transport pattern reverts to one of sodium-linked substrate cotransport, with little or no amiloride-sensitive ENaC activity (3,10,27,33,34).…”

mentioning

confidence: 99%

Aldosterone suppresses expression of an avian colonic sodium-glucose cotransporter

Laverty

Bjarnadóttir

Elbrønd

et al. 2001

American Journal of Physiology-Regulatory, Integrative and Comp

View full text Add to dashboard Cite

Transport in the colon of the domestic fowl switches from sodium-linked hexose and amino acid cotransport on high-salt intake to amiloride-sensitive sodium channel expression on low-salt (LS) diets. The present experiments were designed to investigate the role of aldosterone in suppression of the colonic sodium-glucose luminal cotransporter (SGLT). LS-adapted hens were resalinated with or without simultaneous aldosterone treatment. Changes in the electrophysiological responses and SGLT protein expression levels were examined at 1, 3, and 7 days of treatment. Serum aldosterone levels fell from approximately 400 pmol/l in LS-adapted hens to values below the detection limit (<44 pmol/l) after 1 day of resalination. At the same time, glucose-stimulated short circuit current (I(SC)) increased from 20.9 +/- 8.7 to 56.3 +/- 15.5 microA/cm(2), whereas amiloride-sensitive I(SC) decreased from -68.9 +/- 12.7 microA/cm(2) on LS to +0.6 +/- 12.0 microA/cm(2). Glucose-stimulated I(SC) increased further at 3 and 7 days of resalination, whereas amiloride-sensitive I(SC) remained suppressed. When resalinated birds were simultaneously treated with aldosterone, the LS pattern of high amiloride-sensitive I(SC) and low glucose-stimulated I(SC) was maintained. Immunoblotting results from the same tissues demonstrated that SGLT-like protein expression increased following resalination. Aldosterone treatment completely blocked this effect. These results demonstrate that aldosterone suppresses both activity and protein expression of hen colonic SGLT. Resalination either through decreased aldosterone or other factors may be able to activate SGLT activity independently of increases in protein expression.

show abstract

NaCl-dependent expression of amiloride-blockable Na+ channel in Xenopus oocytes

Cited by 9 publications

References 0 publications

Methylation Increases the Open Probability of the Epithelial Sodium Channel in A6 Epithelia

Methylation Increases the Open Probability of the Epithelial Sodium Channel in A6 Epithelia

Segmental variability of ENaC subunit expression in rat colon during dietary sodium depletion

Aldosterone suppresses expression of an avian colonic sodium-glucose cotransporter

Contact Info

Product

Resources

About