ATP masks stretch activation of epithelial sodium channels in A6 distal nephron cells.

The mechanosensitivity of the epithelial sodium channel (ENaC) is controversial. Using cell-attached patch-clamp techniques, we found that mechanical stretch stimulated ENaC in A6 distal nephron cells in only three of nine cell-attached patches. However, stretch consistently activated ENaC after apical ATP was scavenged with apical hexokinase plus glucose or after P(2) receptors in the patch were blocked. The mean open probability (P(o)) of ENaC was increased from 0.31 +/- 0.04 to 0.61 +/- 0.06 (P < 0.001; n = 9) when patch pipettes contained hexokinase and glucose, or from 0.24 +/- 0.05 to 0.55 +/- 0.11 (P < 0.01; n = 7) when patch pipettes contained suramin, respectively. A poorly hydrolyzable ATP analog, ATPgammaS, in the patch pipettes inhibited ENaC, reducing the P(o) from 0.41 +/- 0.06 to 0.19 +/- 0.05 (P < 0.01; n = 8). Pretreatment of A6 cells with the phospholipase C (PLC) inhibitor U-73122 abolished the effect of ATP on ENaC activity. These data together suggest that ATP, acting through a PLC-dependent purinergic pathway, masks stretch-induced ENaC activation.