Intracellular H+ regulates the alpha -subunit of ENaC, the epithelial Na+ channel |
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Authors: | Chalfant, Michael L. Denton, Jerod S. Berdiev, Bakhram K. Ismailov, Iskander I. Benos, Dale J. Stanton, Bruce A. |
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Abstract: | Protons regulateelectrogenic sodium absorption in a variety of epithelia, including thecortical collecting duct, frog skin, and urinary bladder. Recently,three subunits ( , , ) coding for the epithelial sodium channel(ENaC) were cloned. However, it is not known whether pH regulatesNa+ channels directly byinteracting with one of the three ENaC subunits or indirectly byinteracting with a regulatory protein. As a first step to identifyingthe molecular mechanisms of proton-mediated regulation of apicalmembrane Na+ permeability inepithelia, we examined the effect of pH on the biophysical propertiesof ENaC. To this end, we expressed various combinations of -, -,and -subunits of ENaC in Xenopusoocytes and studied ENaC currents by the two-electrode voltage-clampand patch-clamp techniques. In addition, the effect of pH on the -ENaC subunit was examined in planar lipid bilayers. We report that , , -ENaC currents were regulated by changes in intracellular pH(pHi) but not by changes inextracellular pH (pHo).Acidification reduced and alkalization increased channel activity by avoltage-independent mechanism. Moreover, a reduction ofpHi reduced single-channel openprobability, reduced single-channel open time, and increased single-channel closed time without altering single-channel conductance. Acidification of the cytoplasmic solution also inhibited , -ENaC, , -ENaC, and -ENaC currents. We conclude thatpHi but notpHo regulates ENaC and that the -ENaC subunit is regulated directly bypHi. |
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