Properties of the potassium conductances of principal cells of rat cortical collecting ducts

In this study we examined by impalement techniques properties of the macroscopic K⁺ conductances in the luminal and basolateral membrane of principal cells from isolated perfused cortical collecting ducts (CCD) of the rat. Both membranes possess a dominating K⁺ conductance. Compared to their behaviour with K⁺, both membranes appear much less permeable to NH₄⁺and Rb⁺, and the K⁺ conductances of both membranes are inhibited by these cations. In light of these findings, it is very unlikely that significant amounts of NH₄⁺, which is secreted in the CCD, cross the principal cells as NH₄⁺. Several inhibitors with known effects on K⁺ channels in patch-clamp studies have been examined. Tetraethylammonium, which inhibits the excised K⁺ channels of these cells, has no effect on the macroscopic K⁺ conductances of either membrane. Verapamil, which inhibits the K⁺ channels in the luminal membrane, acts predominantly on the basolateral membrane K⁺ conductance in the intact tubule. Therefore, some of the macroscopic properties of the K⁺ conductances are distinct from those of single channels thus far observed in patchclamp studies.Supported by DFG Schl 277/2-1 and Gr 480/10