Stimulation by aldosterone of a conductive chloride pathway in toad skin.
As a rule, chloride movement (JC1-) across amphibian skin is considered to be passive; this is implied in fact for preparations incubated in Ringer's fluid, since short-circuit current (Isc) is the quantitative expression of net, active sodium transport (JNa+). The nature of the Cl- pathway(s) was investigated by incubating amphibian skin (mostly Bufo marinus) with Cl- present on the epithelial side only, and after blocking JNa+ by combined treatment with ouabain and amiloride. In such conditions, JCl- was found to be equal to (reversed) Isc; furthermore, when JCl- was "translated" in terms of conductance, gCl-, the latter accounted almost quantitatively for transepithelial conductance, g1. When residual intratissue (i.e. intracellular) electronegativity was eliminated by replacing Na+ with K+, JCl- was larger but Isc and JCl- were still found to reflect each other, and gCl- again accounted for most, if not all, of g1. JCl- in the opposite direction, as a result of Cl- being present only on the dermal side, was negligible, and g1 was very low. Thus, in the absence of sodium transport, when experimental conditions are such that a net inward JCl- obtains, the anion apparently flows only through (a) conductive pathway(s). Aldosterone is probably involved in the regulation of this pathway, as JCl- was much lower when toads were maintained in dilute saline than in water or on moist peat; so was the fraction of the apical surface corresponding to mitochondria-rich cells.
Crabbe
J
J
Department of Physiology, University of Louvain (UCL) Medical School, Brussels, Belgium.
Beaujean
V
V
Devuyst
O
O
D000450:Aldosterone / Q000494:pharmacology*; D000818:Animals; D002024:Bufo marinus; D018118:Chloride Channels; D002712:Chlorides / Q000378:metabolism*; D004553:Electric Conductivity; D004848:Epithelium / Q000187:drug effects / Q000502:physiology; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D008565:Membrane Proteins / Q000378:metabolism*; D012867:Skin / Q000187:drug effects; D012879:Skin Physiological Phenomena
D018118:Chloride Channels; D002712:Chlorides; D007473:Ion Channels; D008565:Membrane Proteins; D000450:Aldosterone