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Journal of Experimental Biology, Vol 174, Issue 1 235-246, Copyright © 1993 by Company of Biologists

JOURNAL ARTICLES

Bulk flow of the medium and cutaneous sodium uptake in frogs: potential significance of sodium and oxygen boundary layers

ME Feder, RJ Gonzalez, T Robbins and CR Talbot
Department of Organismal Biology and Anatomy, University of Chicago, IL 60637.

To examine the potential impact of fluid dynamic boundary layers on cutaneous ion exchange, we investigated how bulk flow of dilute Na+ solutions (< or = 1.0 mmol l-1) over the skin of intact frogs (Rana catesbeiana and Rana pipiens) affects cutaneous Na+ uptake (JNa(in)) and transepithelial potential (TEP). Cessation of stirring resulted in a 14-35% decrease in TEP and a 14-65% decrease in JNa(in). Two weeks' acclimation to an unstirred bath increased JNa(in) to levels 70% greater than in frogs acclimated to a continuously stirred bath and to levels comparable to those of frogs acclimated to deionized water. These effects are consistent with depletion of Na+ in the boundary layer, but are also consistent with depletion of O2 in the boundary layer, which might limit generation of ATP consumed by ATPases responsible for cutaneous Na+ uptake. To investigate this latter possibility, we measured TEP and JNa(in) while manipulating the PO2 of well-stirred external media at constant [Na+]. Hyperoxia (PO2 > or = 97 kPa) increased JNa(in) by 28% and had little or no effect on TEP. Hypoxia (PO2 < or = 1.5 kPa) reduced JNa(in) by 48% and decreased TEP by 22%. These results suggest that ionic and gaseous boundary layers may interact to affect cutaneous ion transport.




© The Company of Biologists Ltd 1993