Role of Na-K-atpase in the renal reabsorption of sodium in the elasmobranch, squalus acanthias

1. 1. The relative importance of Na-K-activated ATPase in active bulk transport of Na + in the elasmobranch kidney was examined. Fractional Na + excretion was examined before and after the administration of ouabain, associated with over a 60 per cent reduction in enzyme activity, as well as following furosemide and ethacrynic acid. 2. 2. Marked inhibition of Na-K-ATPase with ouabain did not reduce Na + reabsorption, in contrast to furosemide and ethacrynic acid which increased fractional excretion from 0·22 to 0·69. 3. 3. These data suggest that Na-K-ATPase does not participate in bulk transport of Na + in the elasmobranch kidney, where the conservation of Na + is of little importance in osmoregulation.