Brush-border membrane cation conducting channels from rat kidney proximal tubules.

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).