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Isolated perfused tubule; Rabbit cortical thick ascending limb of Henle's loop; Sodium potassium-chloride cotransport; Ba2+
Abstract:
Previous data from our laboratory have shown that active transport in the cortical thick ascending limb of Henle's loop (cTAL), as measured by the short circuit current (Lsc, microA X cm−2), requires the presence of Na+ and Cl−. The data were compatible with the model of secondarily active Cl− reabsorption involving the cotransport of Na+ and Cl− across the luminal membrane. The data suggested, furthermore, that 1 Na+ and 2 Cl− interact with the luminal carrier. In the present study it was tested whether this reabsorptive mechanism also requires the presence of luminal K+. Isolated cTAL segments (n = 40) were perfused at high flow rates with a modified Ringer's solution. Removal of K+ from the lumen reduced Isc significantly from 215 to 133 microA X cm−2. Addition of Ba2+ (10−3 mol X 1−1) which blocks the K+ conductance of the luminal, membrane, to the K+-containing lumen perfusate decreased Isc significantly from 234 to 141 microA X cm−2. Combination of both manoeuvres: perfusion with a K+-free and Ba2+-containing solution almost abolished Isc from a control of 237 to 56 microA X cm−2. The results are compatible with the view that in rabbit cTAL the luminal carrier interacts with all 3 ions, possibly 1 Na+, 2 Cl−, and 1 K+. K+ recycles across the luminal membrane through its conductive pathway.
