Effects of ouabain on potassium transport in the perfused bullfrog kidney

We studied the effect of ouabain on transepithelial and cellular potassium transport in the isolated perfused bullfrog kidney. We used recently developed techniques for estimating the unidirectional reabsorptive and secretory K fluxes (Jr and Js) and measuring the kinetics of cellular K transport. Two hours of perfusion with 1 X 10(-6) M ouabain did not affect GFR, reduced fractional Na reabsorption 57%, increased K excretion 41%, and inhibited Jr 34%. Js rose 68% at 60 min and then returned to the control level. Ninety minutes of perfusion with 5 X 10(-6) M ouabain reduced GFR 28% and fractional Na reabsorption 76%. K excretion rapidly increased 71% within 30 min and then fell to 60% of the control level, while Jr fell 64%. Js rose 42% in 30 min and then fell to 23% of the control level. Both doses reduced K uptake into cellular pools from the circulation and increased the rate coefficients for efflux into tubular fluid. The data indicate that ouabain inhibited reabsorption and transiently accelerated the rate of loss of K from the cells into the tubular fluid. This initially masked the ultimate inhibition of K secretion from the circulation into the tubular fluid.