Transport of Potassium-42 and Rubidium-86 by Kidney Cortex Slices: the Effect of Varied Concentration Gradients

Abstract

A COMPARISON of the transport of potassium with that of rubidium has been made in earlier work¹, in which some evidence was obtained that, in contrast to sodium, the transport of both potassium and rubidium across the membrane of renal tubular cells is determined only by electrochemical gradients. A deficiency in this work was that the rubidium content of tissue slices had to be estimated from differences in potassium content as compared with control slices. For this reason, the experiments have been repeated using potassium-42 and rubidium-86, to give a direct estimation, both being present only in the incubating medium (a modified Krebs–Ringer phosphate medium containing the indicated concentrations of potassium and rubidium, with 0.005 M alpha-keto glutarate as substrate, at 25° C.). Activity was measured in neutralized nitric acid digests of tissue slice samples, using aluminium dishes, with values corrected for decay, dilution, extracellular space, etc. Since the specific activities of the two isotopes were different by a factor of 4.0, the rubidium counts were arbitrarily divided by this factor to give a better comparison of results. Isotope measurements for rubidium-86 in samples containing both potassium-42 and rubidium-86 were carried out five days after the actual experiment, at which time potassium-42 activity was nil. Measurements of potassium-42 activity in tissue samples were not complicated by the presence of rubidium-86. Details of composition of the media are given in ref. 1.