Kinetic analysis of potassium transport in bullfrog kidney.

Techniques have been developed for studying the distribution and the rates of exchange of K among urine, the tubular cells, and the circulation in the isolated, pump-perfused, bullfrog kidney. Tubular cells were loaded with 42K via the portal circulation, and the subsequent washout of the tracer into the vena cava and into urine was measured. Analysis of the data indicated the existence of at least three cellular pools of K. Pools a and b have half times of exchange of 1.1 and 4.1 min and contain about 25 and 40% of tissue K, respectively. The remainder of cellular K is contained in one or more very slowly exchanging pools. The rate of exchange of K at the basolateral surface of tubular cells is 50-fold greater than at the luminal surface. A pulse-washout method was also devised to permit control and experimental measurements to be made in the same kidney. With this technique, we found that portal perfusion with 10 mM K increased the rate of uptake into pools a and b from the circulation and the rate constants for efflux into the urine from both pools, Acetazolamide increased uptake into pool a and the rate constants for efflux into the urine from both pools.