Mechanism of potassium transport across proximal tubule epithelium in the rat

The mechanism of proximal tubule potassium reabsorption was studied by stopped-flow microperfusion and determination of potassium activities by ion-sensitive resin microelectrodes. The proximal tubule was unable to establish transepithelial potassium gradients. perfusion with 20 mM K+ turned the lumen 3 mV more negative, an effect abolished by Ba2+. the half-time for K+ activities to reach their stationary level after perfusion with 1 mMK+ was significantly increased by Ba2+ from 4.25 ñ 0.14sto 11.0 ñ 1.71s, and aftr perfusion with 20 mMK+, from 5.43 ñ 0.20 to 12.53 ñ 0.90s. These data indicate that a significant fraction of potassium is transferred across proximal tubule spithelium by a transcellular, K+-channel-dependent route