title: Mammalian ASIC2a and ASIC3 subunits co-assemble into heteromeric proton-gated channels sensitive to Gd3+.
abstract: Proton receptors of the acid-sensing ion channel (ASIC) family are expressed in sensory neurons and thus could play a critical role in the detection of noxious acidosis. To investigate the subunit composition of native ASICs in peripheral and central neurons, we co-injected human as well as rodent ASIC2a and ASIC3 subunits in Xenopus oocytes. The amplitudes of acid-induced biphasic responses mediated by co-expressed ASIC2a and ASIC3 subunits were much larger (as much as 20-fold) than the currents mediated by the respective homomers, clearly indicating functional association. The reversal potential of the ASIC2a+3 current (>/=+20 mV) reflected a cationic current mainly selective for sodium. The sensitivity to pH or amiloride of single versus co-expressed ASIC subunits was not significantly different; however, gadolinium ions inhibited ASIC3 and ASIC2a+3 responses with much higher potency (IC(50) approximately 40 microm) than the ASIC2a response (IC(50) >/=1 mm). Biochemical interaction between ASIC2a and ASIC3 subunits was demonstrated by co-purification from transfected human embryonic kidney (HEK293) cells and Xenopus oocytes. Our in situ hybridization data showed that rat ASIC2a and ASIC3 transcripts are co-localized centrally, whereas reverse transcription-polymerase chain reaction data led us to detect co-expression of human ASIC2a and ASIC3 subunits in trigeminal sensory ganglia, brain, and testis where they might co-assemble into a novel subtype of proton-gated channels sensitive to gadolinium.
authors.affiliation: Cell Biology of Excitable Tissue Group, Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada H3A 2B4.
authors.forename: K
authors.initials: K
authors.lastname: Babinski
authors.forename: S
authors.initials: S
authors.lastname: Catarsi
authors.forename: G
authors.initials: G
authors.lastname: Biagini
authors.forename: P
authors.initials: P
authors.lastname: Séguéla
mesh_terms: D062565:Acid Sensing Ion Channels; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D062626:Degenerin Sodium Channels; D053503:Epithelial Sodium Channels; D005260:Female; D005682:Gadolinium / Q000494:pharmacology*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007473:Ion Channels / Q000737:chemistry* / Q000187:drug effects / Q000235:genetics; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000187:drug effects / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D014982:Xenopus laevis
chemical_list: C568424:ASIC2 protein, human; D062565:Acid Sensing Ion Channels; C568425:Asic2 protein, rat; D062626:Degenerin Sodium Channels; D053503:Epithelial Sodium Channels; D007473:Ion Channels; D009419:Nerve Tissue Proteins; D012333:RNA, Messenger; D000584:Amiloride; D005682:Gadolinium