Potassium and rubidium transport by the rabbit ccd rubidium reduces potassium conductance and sodium transport
Warden, D.H.; Hayashi, M.; Schuster, V.L.; Stokes, J.B.
American Journal of Physiology 257(1 Part 2): F43-F52
We compared transport of K+ and Rb+ across the rabbit cortical collecting duct to gain insight into the mechanisms of K+ secretion. Passive tracer fluxes, active secretory rates, electrophysiological behavior, and the ability of each ion to support Na+-K+ ATPase activity were determined. When active transport was inhibited by amiloride, K+ permeability was twice the Rb+ permeability. Transepithelial conductance (GT) was half as great in solutions were 5 mM Rb+ replaced 5 mM K+. When 4 mM Ba2+ was added to the lumen, both Rb+ and K+ permeability fell to values not different from that expected for paracellular diffusion. The relationship between Ba2+-induced changes in the K+ and Rb+ permeabilities and in the simulatenously measured GT provides strong evidence that K+ transport across the apical membrane is largely, if not exclusively, conductive. We also determined that net K+ secretion is greater htan net Rb+ secretion (when each is the abundant ion). the reasons for this difference probably involve several steps in the K+ secretory process and include the following: 1) reduced ATPase activity in the presence of Rb+ (.apprx.80%) compared with K+, 2) reduction of Na+ absorption, and 3) partial blockade of the apical (and perhaps basolateral) K+ conductance. Although ther e were quantitative differences between K+ and Rb+ transprot, we found no evidence suggesting that these ions are transported by different mechanisms.