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Departments of Medicine and of Physiology, Tulane University School of Medicine, New Orleans, Louisiana 70112
The effect of extracellular acidification was tested on the native epithelial Na+ channel (ENaC) in A6 epithelia and on the cloned ENaC expressed in Xenopus oocytes. Channel activity was determined utilizing blocker-induced fluctuation analysis in A6 epithelia and dual electrode voltage clamp in oocytes. In A6 cells, a decrease of extracellular pH (pHo) from 7.4 to 6.4 caused a slow stimulation of the amiloride-sensitive short-circuit current (INa) by 68.4 ± 11% (n = 9) at 60 min. This increase of INa was attributed to an increase of open channel and total channel (NT) densities. Similar changes were observed with pHo 5.4. The effects of pHo were blocked by buffering intracellular Ca2+ with 5 µM 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid. In oocytes, pHo 6.4 elicited a small transient increase of the slope conductance of the cloned ENaC (11.4 ± 2.2% at 2 min) followed by a decrease to 83.7 ± 11.7% of control at 60 min (n = 6). Thus small decreases of pHo stimulate the native ENaC by increasing NT but do not appreciably affect ENaC expressed in Xenopus oocytes. These effects are distinct from those observed with decreasing intracellular pH with permeant buffers that are known to inhibit ENaC.
epithelial sodium channel; A6 epithelia; Xenopus oocytes; noise analysis; channel density
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