The kinetics and distribution of potassium in the toad bladder

Summary Short-circuited toad bladders were loaded with K⁴² from the serosal medium in a chamber stirred by rotating impellers. The chambers were washed with nonradioactive Ringer's, and all effluent was collected from the two chambers separately for 30-sec intervals for 30 min and counted. Count rate data were fitted to sums of exponentials and analyzed by the methods of compartmental analysis. There are at least two potassium compartments, with half times of 2.42 and 18.48 min. These compartments contain 2.01 and 7.93 Equiv×100 mg dry weight^–1, respectively, amounting to 45% of total tissue K. Determinations of the rate of buildup of tracer in the tissue after immersing the bladder in K⁴² Ringer's confirmed the fact that only a portion of tissue K exchanges even after one hr; thus the rest must have a considerably slower exchange rate. Fluxes at the inside border are far greater than at the outside, as predicted from electrophysiological data. Of the two tissue compartments, only the smaller and faster one appears to be related to Na transport, since only this compartment shows changes after Na removal (unidirectional serosal K fluxes decrease by some 50%) or after the addition of vasopressin (serosal fluxes and pool size increase by over two-fold). The results also are consistent with the operation of a 11 Na–K exchange pump at the serosal border.