Vascular aspects of water uptake mechanisms in the toad skin: Perfusion, diffusion, confusion

• Published in: Comparative biochemistry and physiology. Part A, Molecular & integrative physiology Vol. 148; no. 1; pp. 55 - 63
• Main Authors: Willumsen, Niels J., Viborg, Arne L., Hillyard, Stanley D.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.09.2007
• Subjects: Amphibia; Amphibian skin; Animals; Aquaporins; Base Sequence; Blood flow; Bufonidae - physiology; Dehydration; Diffusion; DNA Primers; Osmolar Concentration; Perfusion; Reverse Transcriptase Polymerase Chain Reaction; Seat patch; Skin - blood supply; Skin Physiological Phenomena; Sodium Chloride; Toad; Water uptake; Amphibian skin; Aquaporins; Toad; Water uptake; Seat patch; Dehydration; Blood flow
• ISSN: 1095-6433; 1531-4332
• DOI: 10.1016/j.cbpa.2006.12.032

Blood cell flow (BCF) in the water absorbing “seat patch” region of toad skin was measured with laser Doppler flow cytometry. BCF of dehydrated toads increased by a factor of 6–8 when water contact was made and declined gradually as toads rehydrated. Water absorption was initially stimulated and declined in parallel with BCF. Water absorption measured during the initial rehydration period did not correlate with BCF and hydrated toads injected with AVT increased water absorption without an increase in BCF indicating the lack of an obligate relation between blood flow and water absorption. Aquaporins 1–3 were characterized by RT-PCR analysis of seat patch skin. AQP 1 was localized in the endothelium of subepidermal capillaries and serves as a pathway for water absorption in series with the apical and basolateral membranes of the epithelium. Dehydrated toads rehydrated more rapidly from dilute NaCl solutions than from deionized water despite the reduced osmotic gradient. BCF of toads rehydrating on 50 mM NaCl was not different than on deionized water and blocking Na + transport with 100 μM amiloride did not reduce water absorption from 50 mM NaCl. Thus, neither circulation nor solute coupling explains the greater absorption from dilute salt solutions. Rehydration from 10 mM CaCl 2 was stimulated above that of DI water by a similar degree as with 50 mM NaCl suggesting the anion might control water permeability of the skin.