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1 Division of Nephrology, Department of Medicine, The University of Alabama at Birmingham, Birmingham, Alabama 35294; and 2 Center for Cell and Molecular Signaling, Department of Physiology, Emory University School of Medicine, Atlanta, Georgia 30322
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 P2
receptors in the patch were blocked. The mean open probability
(Po) 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,
ATP
S, in the patch pipettes inhibited ENaC, reducing the
Po 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.
patch-clamp techniques; stretch; autocrine regulation; purinergic receptors; phospholipase C; adenosine 5'-triphosphate
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