Excretion of Na²² and K⁴² by the Perfused Bullfrog Kidney and the Effect of Some Poisons

¹ From the Department of Physiology, University of Minnesota, Minneapolis, Minnesota

Perfusion of the bullfrog (Rana catesbiana) kidney with Na²² and K⁴² via the renal portal system results in a urine with a high content of both isotopes. These isotopes must enter the urine by passing though the wall of the renal tubule or the collecting ducts since glomerular filtration of the portal fluid was negligible. The descending order of equilibration of these radioisotopes and of D₂O is in general from D₂O to K⁴² to Na²². Calculation of the unidirectional-reabsorptive and excretory movements across the tubules suggest that the depression in net reabsorption of sodium and potassium by azide, cyanide, and dinitrophenol is due more to a decrease in the unidirectional reabsorptive movement than to an increase in the excretory movement. The unidirectional excretory movements of sodium and of potassium show no consistent trend during the control periods and continue in the same fashion during the perfusion of the poisons. It is inferred that the excretory movements of sodium and potassium are of a passive nature, or that they depend upon a type of energetic process different from that involved in the reabsorptive movement.