ABSTRACT
To examine the potential impact of fluid dynamic boundary layers on cutaneous ion exchange, we investigated how bulk flow of dilute Na+ solutions (≤1.0mmol l− 1) over the skin of intact frogs (Rana catesbeiana and Rana pipiens) affects cutaneous Na+ uptake 
and transepithelial potential (TEP). Cessation of stirring resulted in a 14–35% decrease in TEP and a 14–65% decrease in 
. Two weeks’ acclimation to an unstirred bath increased 
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 
while manipulating the 
of well-stirred external media at constant [Na+]. Hyperoxia 
increased 
by 28% and had little or no effect on TEP. Hypoxia 
reduced 
by 48% and decreased TEP by 22%. These results suggest that ionic and gaseous boundary layers may interact to affect cutaneous ion transport.
