Ammonium interaction with the epithelial sodium channel.
The purpose of this study was to investigate the direct effect of NH(3)/NH on mouse epithelial Na(+) channels (mENaC) expressed in Xenopus oocytes. Two-electrode voltage-clamp and ion-selective microelectrodes were used to measure the Na(+) current, intracellular pH (pH(i)), and ion activities in oocytes expressing mENaC. In oocytes expressing mENaC, removal of external Na(+) reversibly hyperpolarized membrane potential by 129 +/- 5.3 mV in the absence of 20 mM NH(4)Cl but only by 100 +/- 7.8 mV in its presence. Amiloride completely inhibited the changes in membrane potential. In oocytes expressing mENaC, butyrate (20 mM) caused a decrease in pH(i) (0.43 +/- 0.07) similar to the NH(4)Cl-induced pH(i) decrease (0.47 +/- 0.12). Removal of Na(+) in the presence of butyrate caused hyperpolarization that was not significantly different from that in the absence of butyrate at high pH(i) (in the absence of NH(4)Cl). Removal of external Na(+) resulted in an outward current of 3.7 +/- 0.8 microA (at -60 mV). The magnitude of this change in current was only 2.7 +/- 0.7 microA when Na(+) was removed in the presence of NH(4)Cl. In oocytes expressing mENaC, NH(4)Cl also caused a decrease in whole cell conductance at negative potential and an outward current at positive potential. In the presence of amiloride, steady-state current and the change in current caused by removal of Na(+) were not different from zero. These results indicate that NH(4)Cl inhibits Na(+) transport when mENaC is expressed in oocytes. The inhibition of voltage changes is not due to intracellular acidification caused by NH(4)Cl. Permeability and selectivity of ENaC to NH may play a role.
Nakhoul
N L
NL
Section of Nephrology, Department of Medicine, Tulane University School of Medicine, 1430 Tulane Ave., New Orleans, Louisiana 70112, USA. nakhoul@tulane.edu
Hering-Smith
K S
KS
Abdulnour-Nakhoul
S M
SM
Hamm
L L
LL
D000584:Amiloride / Q000494:pharmacology; D000643:Ammonium Chloride / Q000494:pharmacology*; D000818:Animals; D002087:Butyrates / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D053503:Epithelial Sodium Channels; D005260:Female; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D009865:Oocytes / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011994:Recombinant Proteins / Q000378:metabolism; D015222:Sodium Channels / Q000235:genetics / Q000502:physiology*; D013997:Time Factors; D014982:Xenopus laevis
D002087:Butyrates; D053503:Epithelial Sodium Channels; D011994:Recombinant Proteins; D015222:Sodium Channels; D000643:Ammonium Chloride; D000584:Amiloride