Regulation of single potassium ion channels from apical membrane of rabbit collecting tubule.

The regulation of K+-channel activity from the apical membrane of the rabbit cortical collecting tubule was studied using the patch-clamp technique. Using inside-out patches, channel open probability was determined as a function of calcium and barium concentration and transmembrane potential. Channel open probability was increased by raising bath (cytoplasmic) calcium concentration, with an apparent Ka of 2.4 microM. Mean channel open time also increased during this maneuver. The channel was reversibly inhibited by barium, applied to the cytoplasmic face, with an apparent Ki of 12 microM. Depolarization of the transmembrane potential increased channel open probability. With 1 mM calcium in the bath solution, the open probability was one-half maximal at -55 mV. It is concluded that this channel is the probable route for transcellular K+ secretion by the cortical collecting tubule and that procedures likely to increase intracellular calcium and/or depolarize the apical membrane will cause an increased potassium secretion.