INSULIN-ACTIVATED AMILORIDE-BLOCKABLE NONSELECTIVE CATION AND NA+ CHANNELS IN THE FETAL DISTAL LUNG EPITHELIUM

1. The apical membrane of fetal distal lung epithelium had two types o f amiloride-blockable Na+-permeant cation channels; (1) nonselective c ation (NSC) channel with a single channel conductance of 27 pS and (2) Na+ channel with a single channel conductance of 12 pS around resting membrane potential. 2. The IC50 of amiloride to the Na+ channel was 1 -2 mu M, while the IC50 of amiloride to the NSC channel was less 1 mu M. The open probability of the Na+ channel was about 10-fold larger th an that of the NSC channel. 3. Insulin (100 nM) increased the open pro bability of both channels.