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 (G(T)) was half as great in solutions where 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 simultaneously measured G(T) 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 than 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+ (~80%) compared with K+, 2) reduction of Na+ absorption, and 3) partial blockade of the apical (and perhaps basolateral) K+ conductance. Although there were quantitative differences between K+ and Rb+ transport, we found no evidence suggesting that these ions are transported by different mechanisms.
|Original language||English (US)|
|Journal||American Journal of Physiology - Renal Fluid and Electrolyte Physiology|
|Issue number||1 (26/1)|
|State||Published - 1989|
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