AMILORIDE-SENSITIVE SODIUM-CHANNELS IN RABBIT CORTICAL COLLECTING TUBULE PRIMARY CULTURES

Patch-clamp methodology was applied to principal cell apical membranes of rabbit cortical collecting tubule (CCT) primary cultures grown on collagen supports in the presence of aldosterone (1.5-mu-M). The most frequently observed channel had a unit conductance of 3-5 pS, nonlinear current-voltage (I-V) relationship, Na permeability (P(Na))-to-K permeability (P(K)) ratio > 19:1, and inward current at all applied potentials (V(app)) < +80 mV (n = 41). Less frequently, an 8- to 10-pS channel with a linear I-V curve, P(Na)/P(K) < 5:1, and inward current at V(app) < +40 mV was also observed (n = 7). Luminal amiloride (0.75-mu-M) decreased the open probability (P(o)) for both of these channels. Mean open time for the high-selectivity Na+ channel was 2.1 +/- 0.5 s and for the low-selectivity Na+ channel was 50 +/- 12 ms. In primary cultures grown without aldosterone the high-selectivity Na+ channel was rarely observed (1 of 32 patches). Lastly, a 26- to 35-pS channel, nonselective for Na+ over K+, was not activated by cytoplasmic Ca2+ or voltage nor inhibited by amiloride (n = 17). We conclude that under specific growth conditions, namely permeable transporting supports and chronic mineralocorticoid hormone exposure, principal cell apical membranes of rabbit CCT primary cultures contain 1) both high-selectivity and low-selectivity, amiloride-inhibitable Na+ channels and 2) amiloride-insensitive, nonselective cation channels.