Bulk flow of the medium and cutaneous sodium uptake in frogs: potential significance of sodium and oxygen boundary layers.
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.
Feder
M E
ME
Department of Organismal Biology and Anatomy, University of Chicago, IL 60637.
Gonzalez
R J
RJ
Robbins
T
T
Talbot
C R
CR
D000818:Animals; D008564:Membrane Potentials; D008566:Membranes / Q000378:metabolism*; D008954:Models, Biological; D010100:Oxygen / Q000378:metabolism*; D011892:Rana catesbeiana; D011894:Rana pipiens; D012867:Skin / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*
D012964:Sodium; D010100:Oxygen