Mercury blockage of apical water channels in toad skin (Bufo marinus)

• Published in: The Journal of physiology Vol. 468; no. 1; pp. 741 - 752
• Main Authors: Grosso, A, De Sousa, R C
• Format: Journal Article
• Language: English
• Published: England The Physiological Society 01.08.1993
• Subjects: Amphibia; Animals; Bufo marinus; Bufo marinus - metabolism; Cations, Monovalent - metabolism; Dose-Response Relationship, Drug; Epithelium - drug effects; Epithelium - metabolism; Exocytosis - drug effects; Freshwater; In Vitro Techniques; Isoproterenol - pharmacology; Kinetics; Mercury - administration & dosage; Mercury - pharmacology; Models, Biological; Osmosis - drug effects; Permeability - drug effects; Skin - drug effects; Skin - metabolism; Vasopressins - pharmacology; Water - metabolism
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.1993.sp019798

1. Net water flow (Jw) was continuously monitored across the abdominal skin of the toad Bufo marinus by means of a volumetric, automatic technique. Jw was either averaged over periods of 2 min or taken cumulatively (10 or 30 min periods). 2. The state of high water permeability induced by vasopressin or isoprenaline was reversed (88-89% inhibition of delta Jw after 1 h) by the addition of 10(-3) M HgCl2 (or CH3ClHg) to the external bathing medium. Similarly, pre-exposure of the skins to Hg2+, totally blocked the induction of the hydrosmotic response to the same agents. By itself, Hg2+ exerted only a minor (26%) stimulation of basal Jw. 3. There was a sigmoidal dose-response relationship between the reduction of the hydrosmotic effect of vasopressin (VP) and the concentration of Hg2+ in the external medium, with a half-maximal effect at 1.2 x 10(-4) M HgCl2. 4. Total replacement of Na+ by K+, Rb+ or Cs+ in the Ringer solution, caused a VP-like, hydrosmotic effect that was reversed, or prevented, by exposure to Hg2+ in a manner indistinguishable from that previously seen with vasopressin or isoprenaline. 5. The data point to the presence of a Hg(2+)-sensitive apical water pathway in stimulated epithelia, very probably constituted by water channels similar to those reported in red blood cells, amphibian bladder and mammalian kidney tubules.