Volume flow and electric current coupling in frog skin

Volume flow (Jv), clamp currents (Ic) and membrane resistances at different concentration differences of the impermeant solute sucrose (DCi) have been measured on the isolated ventral skin of Rana esculenta. Jv is a non linear function of DCi and shows a slight but definite dependence on the clamp potential DV, decreasing when the skin is clamped both above and below its spontaneous DV. The DV/Ic characteristics at any DCi are linear. Both the intercepts with the DV and Ic axes decrease with increasing DCi, while their inclination (skin resistance) increases with increasing DCi. Such an increase is greater for DCi > 0 (sucrose in the solution bathing the external skin surface) than for DCi < 0. These results agree with the previous observations by Ussing on the relationship between the osmotic behaviour of the skin and its active Na+ transport and allow the determination of an electrokinetic component of Ic from the phenomenological equation Ic = G(DCi) DV + K(DCi) DCi. A comparable slight electroosmotic component of Jv has been determined from the statistical analysis of the Jv data.