Intracellular potassium activity in the rabbit proximal straight tubule.
Double-barreled liquid ion-exchanger microelectrodes were used to measure basolateral membrane potential (VBL) and intracellular potassium activity (aiK) in superficial proximal straight tubules (sPST) of the rabbit perfused in vitro. The mean +/- SE (number of cells in parentheses) value of VBL was -37.8 +/- 2.49 (20) vM and aiK was 48.6 +/- 2.27 (20) mM. The calculated Nernst equilibrium potential (EK) across the basolateral membrane was -68 mV. Lowering both potassium concentration to 0.1 mM reversibly decreased both VBL and aiK to -12.2 +/- 1.21 (19) mV and 11.3 +/- 1.29 (19) mM, respectively. Bath ouabain (10(-5) resulted in similar changes. These results demonstrate that intracellular potassium is actively accumulated in sPST perfused in vitro and that accumulation results primarily from Na-K-ATPase activity in the basolateral membrane. During recovery from low K bath, the temporal relationship between VBL and aiK and the effects of ouabain and high K bath on recovery are used to demonstrate directly electrogenic pumping. Lowering bath pH to 6.7 (HCO-3 = 5 mM) and the presence of 0.5 mM BaCl2 in the bath resulted in a large and rapid depolarization of VBL with little or no change in aiK. These results suggest that the response of VBL to both maneuvers is caused by a decrease in potassium permeability of the basolateral membrane.
D000818:Animals; D001464:Barium / Q000494:pharmacology; D001693:Biological Transport, Active; D003593:Cytoplasm / Q000378:metabolism; D005260:Female; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D008564:Membrane Potentials; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D011817:Rabbits; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
D001464:Barium; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium