Na⁺ and Cl^- Net Absorption by the Isolated Skin of Rana Esculenta

Abstract

In the last five years, several measurements of ²²Na⁺ influx (J_i) and outflux (J_o) across symmetrical parts of the isolated skin o/Rana esculenta, under permanent short circuitation, were performed in our Institute.

The mean value of the ²²Na⁺ net fluxes (J_i-J_o) exceeded the mean value of the short circuit current measurements (1.14 ± 0.04 versus 0.98 ± 0.02 μEcm^-2-h^-1, 253 experiments).

Since this discrepancy could be due to a concomitant Cl^- net absorption, ³⁶Cl^- unidirectional fluxes were detected under similar experimental conditions. The Cl^- net flux mean value was 0.11 ± 0.02 μE cm^-2-h^-1 (316 experiments) which accounts for 70% of the discrepancy between the Na⁺ net flux and short circuit current. This Cl' net absorption occurred in the absence of electrochemical gradients and was very likely maintained by a Na⁺/K⁺/2Cl^- cotransport located at the outermost membrane of the epithelium. In fact bumetanide challenge (10^-5 M in the external fluid) strongly inhibited ³⁶Cl^- influx and ²²Na⁺ influx across this tissue and cleared off the discrepancy between short circuit current and sodium net flux.

Key Words:

• frog skin
• Na⁺ and Cl^- transport
• bumetanide