AJP - Renal Physiology, Vol 257, Issue 3 328-F335, Copyright © 1989 by American Physiological Society
Brush-border membrane cation conducting channels from rat kidney proximal tubules
S. Marom, D. Dagan, J. Winaver and Y. Palti
Dept. of Physiology and Biophysics, Faculty of Medicine, Technion-Israel Institute of Technology, Haifa.
This is a description and kinetic characterization of cation channels from
rat kidney brush-border membrane vesicles and from apical membranes of
proximal tubule cells in culture. Channel activity was demonstrated and
characterized in both artificial phospholipid bilayers and in tissue
culture. Intermediate conductance, approximately 50 pS, cation-selective
channels were observed by both methods. Channels were characterized by a Na
permeability (PNa)/K permeability (PK) of 1-5:1. Open-channel
current-voltage curves were linear in symmetric 300 mM NaCl. In tissue
culture the gating kinetics are described by two open-time constants and
two closed-time constants. Channel activity was neither voltage nor Ca2+
dependent and the probability of being in the open state ranged from 0.6 to
0.95. In tissue culture experiments the channel demonstrated nonstationary
gating activity. A second, 15-pS cation channel, seen in planar bilayers,
demonstrated a higher selectivity for Na+ with a (PNa/PK ratio of greater
than 10).
