title: Presence of luminal K+, a prerequisite for active NaCl transport in the cortical thick ascending limb of Henle's loop of rabbit kidney.
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.
mesh_terms: D000818:Animals; D001693:Biological Transport, Active; D002286:Carcinoma, Ehrlich Tumor / Q000378:metabolism; D004848:Epithelium / Q000378:metabolism; D005665:Furosemide / Q000494:pharmacology; D007672:Kidney Cortex / Q000378:metabolism*; D007684:Kidney Tubules / Q000378:metabolism*; D008138:Loop of Henle / Q000378:metabolism*; D011188:Potassium / Q000502:physiology*; D011817:Rabbits; D012965:Sodium Chloride / Q000378:metabolism*; D013997:Time Factors
chemical_list: D012965:Sodium Chloride; D005665:Furosemide; D011188:Potassium