Potassium permeability of luminal and peritubular membranes in the proximal tubule of bullfrog kidneys.
Using double-barreled K(+)-selective or conventional voltage microelectrode, K+ permeability of the luminal membrane of renal proximal tubule was investigated in comparison with that of the peritubular membrane in doubly-perfused bullfrog kidneys. A decade change in K+ concentration of the luminal perfusate from 3.5 (control) to 35 mM (high K+) induced depolarization in the luminal membrane potential by 11.2 mV with a slight elevation of intracellular K+ activity, (K)i, while those of the peritubular perfusate depolarized peritubular membrane potential by 31.6 mV with a moderate rise of (K)i by 8.0 mEq. The transport number for K+ (tK) in the luminal membrane was about one-third of that in the peritubular membrane. Both luminal and peritubular administrations of Ba2+ (4 mM) additively depolarized membrane potential. The magnitude of Ba2(+)-induced depolarization in the luminal membrane was about one-fourth of that in the peritubular membrane. The high K(+)-induced depolarization elicited from one-side perfusion was hardly affected by Ba2+ which was given from the other side. From these results we conclude that the transport number of K+ in the luminal and peritubular membranes of the proximal tubular epithelium is in the range of 0.17-0.32 and 0.52-0.66, respectively.
Kubokawa
M
M
Department of Physiology, Osaka Medical College, Takatsuki, Japan.
Kubota
T
T
Fujimoto
M
M
D000818:Animals; D001464:Barium / Q000494:pharmacology; D002463:Cell Membrane Permeability / Q000187:drug effects; D004553:Electric Conductivity; D066298:In Vitro Techniques; D007424:Intracellular Fluid / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D010477:Perfusion; D011188:Potassium / Q000378:metabolism*; D011892:Rana catesbeiana
D001464:Barium; D011188:Potassium