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Intracellular H + regulates the α-subunit of ENaC, the epithelial Na + channel

1999; American Physical Society; Volume: 276; Issue: 2 Linguagem: Inglês

10.1152/ajpcell.1999.276.2.c477

1522-1563

Michael L. Chalfant, Jerod S. Denton, Bakhrom K. Berdiev, Iskander I. Ismailov, Dale Benos, Bruce A. Stanton,

Ion Channels and Receptors

Protons regulate electrogenic sodium absorption in a variety of epithelia, including the cortical collecting duct, frog skin, and urinary bladder. Recently, three subunits (α, β, γ) coding for the epithelial sodium channel (ENaC) were cloned. However, it is not known whether pH regulates Na + channels directly by interacting with one of the three ENaC subunits or indirectly by interacting with a regulatory protein. As a first step to identifying the molecular mechanisms of proton-mediated regulation of apical membrane Na + permeability in epithelia, we examined the effect of pH on the biophysical properties of ENaC. To this end, we expressed various combinations of α-, β-, and γ-subunits of ENaC in Xenopusoocytes and studied ENaC currents by the two-electrode voltage-clamp and patch-clamp techniques. In addition, the effect of pH on the α-ENaC subunit was examined in planar lipid bilayers. We report that α,β,γ-ENaC currents were regulated by changes in intracellular pH (pH i ) but not by changes in extracellular pH (pH o ). Acidification reduced and alkalization increased channel activity by a voltage-independent mechanism. Moreover, a reduction of pH i reduced single-channel open probability, reduced single-channel open time, and increased single-channel closed time without altering single-channel conductance. Acidification of the cytoplasmic solution also inhibited α,β-ENaC, α,γ-ENaC, and α-ENaC currents. We conclude that pH i but not pH o regulates ENaC and that the α-ENaC subunit is regulated directly by pH i .