Degenerin sites mediate proton activation of deltabetagamma-epithelial sodium channel.
The delta-subunit of epithelial Na(+) channels (ENaC) is predominately expressed in brain, heart, and pancreas. The amiloride sensitivity, Na(+) conductance, and critical domains for gating are characterized as a cross between proton-activated Na(+) channels and alpha-ENaC. The hypothesis that external protons may activate human delta-ENaC was addressed by expressing deltabetagamma-hENaC in Xenopus oocytes and evaluating proton-activated current with the two-electrode voltage clamp technique. Our results showed that protons transiently evoked a Na(+) current with an EC(50) of pH 6 overlapped on the basal current of deltabetagamma-hENaC. Proton-activated current was not observed in uninjected oocytes. Studies on gating kinetics revealed that activation, desensitization, and recovery times of proton-activated Na(+) current were 3.8 +/- 0.5 s, 253 +/- 9.5 s, and 10 +/- 3.6 s, respectively (n = 4-12). Alkali metal cation selectivity of the proton-activated current was identical to that of the basal current of deltabetagamma-hENaC. The metabolic acids, lactate, pyruvate, and formate, modified the proton-activated current, as did hypo-osmotic stress. EDTA, hypo-osmolarity, and lactate enhanced proton activation synergistically. Our results suggest that delta-hENaC subunit is essential for proton-activated current and gamma-subunit may potentially regulate the response of delta-hENaC to protons. We have concluded that deltabetagamma-hENaC is a proton-activated cation channel whose closing gate can be regulated by a proton-induced conformational change. Proton-sensitivity of deltabetagamma-hENaC may be an important mechanism for integrating external ischemic signals in inflamed and hypoxic tissues.
Ji
Hong-Long
HL
Department of Physiology and Biophysics, University of Alabama at Birmingham, Birmingham, Alabama 35294-0005, USA. ji@physiology.uab.edu
Benos
Dale J
DJ
D062565:Acid Sensing Ion Channels; D000584:Amiloride / Q000494:pharmacology; D019943:Amino Acid Substitution; D000818:Animals; D062626:Degenerin Sodium Channels; D004492:Edetic Acid / Q000494:pharmacology; D053503:Epithelial Sodium Channels; D005561:Formates / Q000494:pharmacology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D007473:Ion Channels / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D019344:Lactic Acid / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D021122:Protein Subunits; D011522:Protons; D019289:Pyruvic Acid / Q000494:pharmacology; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012964:Sodium / Q000502:physiology; D015222:Sodium Channels / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D013329:Structure-Activity Relationship; D014981:Xenopus
C568424:ASIC2 protein, human; D062565:Acid Sensing Ion Channels; D062626:Degenerin Sodium Channels; D053503:Epithelial Sodium Channels; D005561:Formates; D007473:Ion Channels; D009419:Nerve Tissue Proteins; D021122:Protein Subunits; D011522:Protons; D011994:Recombinant Proteins; D015222:Sodium Channels; C030544:formic acid; D019344:Lactic Acid; D000584:Amiloride; D019289:Pyruvic Acid; D004492:Edetic Acid; D012964:Sodium