Site of action of a uremic serum fraction inhibiting sodium transport in frog skin.

The rate coefficients and fluxes of sodium across the outside and inside barriers of an in vitro, short-circuited frog skin preparation were determined in the presence of a uremic serum fraction to localize the site of action of an inhibitor of sodium transport. In unpaired studies, the mean depression of short-circuit current (SCC) resulting from the addition of the uremic serum fraction (21.9+/-2.2%) was significantly greater than the decrease in SCC resulting from either frog Ringer's wash or normal serum fractions. Paired studies comparing active and inactive uremic serum fractions indicated that the reduction in net sodium transport, whether calculated from changes in SCC(-0.55+/-0.12muEq/h) or changes in unidirectional Na fluxes (-0.56+/-0.15 muEq/h) was significantly greater in hemi-skins treated with the active fraction. The depression in sodium transport was associated with a significant decrease of sodium movement from the skin to the inside compartment, phi22 (-0.62+/-0.2 muEq/h). The results of these studies suggest that the inhibition of sodium transport ascribed to the uremic serum fraction is due to an inhibition of the active transport mechanism located at the serosal barrier.