Single-channel recordings from amiloride-sensitive epithelial sodium channel.

We report here the first evidence in intact epithelial cells of unit conductance events from an amiloride-sensitive Na+ channel. The events were observed when patch-clamp recordings were made from the apical surface of cultured epithelial kidney cells (A6). The channel characteristics are as follows. Single-channel conductance ranged between 7 and 10 pS (mean = 8.4 +/- 1.3), the current-voltage (I-V) relationship displayed little if any nonlinearity over a range of +/- 80 mV (with respect to the patch pipette), and the channel Na+/K+ selectivity was approximately 3-4:1. Amiloride, a cationic blocker of the channel, reduced channel mean open time and increased channel mean closed time as the voltage of the cell interior was made more negative. Amiloride induced channel flickering at increased negative potentials (intracellular potential with respect to the patch) but did not alter the single-channel conductance or the I-V relationship from that observed in control patches.