ISSN:
1432-2013
Keywords:
Toad bladder
;
Toad skin
;
Water transport
;
Hydrosmotic response
;
Cyclic adenosine monophosphate
;
Serosal hypertonicity
;
Na+-free media
;
Bufo marinus
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract The vasopressin (VP)-induced increase in water permeability in high-resistance, amphibian epithelia is not altered by the abolition of net Na+ flux caused by amiloride added to the apical bathing medium. In this work we looked at the effects on water transport of amiloride added to the serosal medium at a concentration (10−3 M) known to inhibit Na+/H + exchange. In urinary bladders of Bufo marinus, amiloride partially blocked the hydrosmotic response to VP. A similar inhibition was found with cyclic adenosine 5′-monophosphate (cAMP) or serosal hypertonicity. We hypothesized that this effect of amiloride could be due to an inhibition of Na+/H+ and/or Na+/Ca2+ antiporters present in the epithelial basolateral membrane and looked at the effects of the diuretic in Na+-free media. A similar degree of inhibition of water flow was still found, thus showing that amiloride acts on a cell target other than the antiporters. In toad skin, amiloride did not inhibit the hydrosmotic response to VP and to isoproterenol; however the response to high K+ was significantly reduced. Among the amiloride cell targets described so far, adenylate cyclase and protein kinase A appear to be the best candidates to explain the inhibition of the hydrosmotic response reported here. Direct measurements of intracellular cAMP are needed however to substantiate this hypothesis.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00370700
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