Pathways of K+ permeation across the rabbit cortical collecting tubule: effect of amiloride.
These experiments were designed to examine passive K+ transport by the rabbit cortical collecting tubule. Potassium diffusion voltages were used to assess the presence of apical and basolateral K+ conductances. With amiloride (0.1 mM) in the lumen, reproducible K+ diffusion voltages from both the lumen and bath were obtained. Amiloride enhanced the magnitude of these voltage deflections (delta VT). There were time-dependent increases in the K+ diffusion voltage but the steady-state values were highly reproducible in the same tubule. In the amiloride-treated tubules, delta VT induced by raising bath [K+] to 20 mM was larger than that produced by the same increase in lumen [K+]. To evaluate whether the amiloride-treated tubule had, as suggested by the K+ diffusion voltages, substantial K+ permeabilities on both apical and basolateral membranes, the K+ rate coefficient (lumen-to-bath, KK) was measured before and after amiloride treatment. The amiloride-induced increase in KK, from 66 +/- 6 to 205 +/- 35 nm/s, was significantly larger than could be accounted for by the changes in transepithelial voltage or membrane voltages alone. This discrepancy could be due to single-file diffusion across the apical membrane and/or the (secondary) enhancement of K+ permeability following inhibition of Na+ transport.
D000584:Amiloride / Q000494:pharmacology*; D000818:Animals; D001692:Biological Transport; D004553:Electric Conductivity; D005260:Female; D007684:Kidney Tubules / Q000378:metabolism*; D007685:Kidney Tubules, Collecting / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008433:Mathematics; D010477:Perfusion; D010539:Permeability; D011188:Potassium / Q000378:metabolism*; D011719:Pyrazines / Q000494:pharmacology*; D011817:Rabbits
D011719:Pyrazines; D000584:Amiloride; D011188:Potassium