Fig. 1.

Single Na⁺ channel characteristics in normal and cystic fibrosis (CF) human small airway epithelial cells (hSAECs). A: cell-attached patch-clamp analysis of normal hSAECs; 1 μM amiloride was backfilled into the patch electrode. Downward deflections from arrows (indicating closed-channel state) represent inward current; upward deflections from closed state represent outward current; # demarks a break in the continuous trace; near the 10.5-min mark, amiloride has reached the cell membrane and begins to block Na⁺ current. B and C: highly selective cation (HSC, 6.5 pS) and nonselective cation (NSC, 16.6 pS) channel conductances (γ) calculated from representative trace in A before amiloride inhibition. Both conductances have been shown to be amiloride-sensitive current in lung epithelia (7). D: complete amiloride inhibition of Na⁺ current at 0 and −20 mV (−V_p). Application of polarized potentials of +20, +40, and −60 mV (−V_p) induced current in the presence of amiloride, as expected, although current amplitudes were smaller. E and F: distribution of single-channel conductances from normal (E) and CF (F) hSAECs.