Molecular cloning and regional distribution of a human proton receptor subunit with biphasic functional properties.
Small changes of extracellular pH activate depolarizing inward currents in most nociceptive neurons. It has been recently proposed that acid sensitivity of sensory as well as central neurons is mediated by a family of proton-gated cation channels structurally related to Caenorhabditis elegans degenerins and mammalian epithelial sodium channels. We describe here the molecular cloning of a novel human proton receptor, hASIC3, a 531-amino acid-long subunit homologous to rat DRASIC. Expression of homomeric hASIC3 channels in Xenopus oocytes generated biphasic inward currents elicited at pH <5, providing the first functional evidence of a human proton-gated ion channel. Contrary to the DRASIC current phenotype, the fast desensitizing early component and the slow sustained late component differed both by their cationic selectivity and by their response to the antagonist amiloride, but not by their pH sensitivity (pH50 = 3.66 vs. 3.82). Using RT-PCR and mRNA blot hybridization, we detected hASIC3 mRNA in sensory ganglia, brain, and many internal tissues including lung and testis, so hASIC3 gene expression was not restricted to peripheral sensory neurons. These functional and anatomical data strongly suggest that hASIC3 plays a major role in persistent proton-induced currents occurring in physiological and pathological conditions of pH changes, likely through a tissue-specific heteropolymerization with other members of the proton-gated channel family.
Babinski
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Cell Biology of Excitable Tissue Group, Montreal Neurological Institute, McGill University, Quebec, Canada.
Lê
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KT
Séguéla
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D062565:Acid Sensing Ion Channels; D000584:Amiloride / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D004232:Diuretics / Q000494:pharmacology; D004558:Electric Stimulation; D004594:Electrophysiology; D015870:Gene Expression; D006863:Hydrogen-Ion Concentration; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000032:analysis / Q000235:genetics; D009475:Neurons, Afferent / Q000737:chemistry* / Q000502:physiology; D009865:Oocytes / Q000502:physiology; D011522:Protons; D015222:Sodium Channels / Q000032:analysis* / Q000235:genetics*; D014278:Trigeminal Nuclei / Q000166:cytology; D014982:Xenopus laevis
C112231:ASIC3 protein, human; C568269:ASIC3 protein, rat; D062565:Acid Sensing Ion Channels; D004232:Diuretics; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D011522:Protons; D015222:Sodium Channels; D000584:Amiloride