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Acid-sensing ion channel (ASIC) 1a/2a heteromers have a flexible 2:1/1:2 stoichiometry.

ABSTRACT: Acid-sensing ion channels (ASICs) are widely expressed proton-gated Na(+) channels playing a role in tissue acidosis and pain. A trimeric composition of ASICs has been suggested by crystallization. Upon coexpression of ASIC1a and ASIC2a in Xenopus oocytes, we observed the formation of heteromers and their coexistence with homomers by electrophysiology, but could not determine whether heteromeric complexes have a fixed subunit stoichiometry or whether certain stoichiometries are preferred over others. We therefore imaged ASICs labeled with green and red fluorescent proteins on a single-molecule level, counted bleaching steps from GFP and colocalized them with red tandem tetrameric mCherry for many individual complexes. Combinatorial analysis suggests a model of random mixing of ASIC1a and ASIC2a subunits to yield both 2:1 and 1:2 ASIC1a:ASIC2a heteromers together with ASIC1a and ASIC2a homomers.

SUBMITTER: Bartoi T

PROVIDER: S-EPMC4050600 | biostudies-literature | 2014 Jun

REPOSITORIES: biostudies-literature

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Acid-sensing ion channel (ASIC) 1a/2a heteromers have a flexible 2:1/1:2 stoichiometry.

Bartoi Tudor T Augustinowski Katrin K Polleichtner Georg G Gründer Stefan S Ulbrich Maximilian H MH

Proceedings of the National Academy of Sciences of the United States of America 20140520 22

Acid-sensing ion channels (ASICs) are widely expressed proton-gated Na(+) channels playing a role in tissue acidosis and pain. A trimeric composition of ASICs has been suggested by crystallization. Upon coexpression of ASIC1a and ASIC2a in Xenopus oocytes, we observed the formation of heteromers and their coexistence with homomers by electrophysiology, but could not determine whether heteromeric complexes have a fixed subunit stoichiometry or whether certain stoichiometries are preferred over ot ...[more]

PMID: 24847067

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Project description:IntroductionIrritable bowel syndrome and bladder pain syndrome are both characterized by pain in response to organ distension. Epidemiologic studies showed that these two syndromes are often overlapped. Such overlap may be due to sharing of common extrinsic innervations between the colorectum and the urinary bladder, where cross-sensitization of the urinary bladder and the colon would occur in response to mechanical distension of either organ. The aim of this project was to develop and characterize a rodent model of urinary bladder-colon sensitization and to assess the role of the acid sensing ion channel (ASIC)-3.MethodsDouble retrograde labelling was performed to identify extrinsic primary afferent neurons innervating both the colon (Fluororuby) and urinary bladder (Fluorogold) in the L6-S1 dorsal root ganglia (DRG) in Sprague Dawley rats. The phenotype of the colon/urinary bladder co-innervating primary afferent neurons was assessed using immunohistochemistry directed against ASIC-3. Cross-organ sensitization was induced in Sprague Dawley rats by using an echography-guided intravesical administration of acetic acid (0.75%) under brief isoflurane anesthesia. Colonic sensitivity was assessed in conscious rats by measuring abdominal contraction during isobaric colorectal distension (CRD). Measurement of urinary bladder and colonic paracellular permeabilities and tissue myeloperoxidase assay were performed. The involvement of ASIC-3 was assessed by use of S1 intrathecal administration of the ASIC-3 blocker, APETx2 (2.2 µM).ResultsImmunohistochemistry showed that 73.1% of extrinsic primary afferent neurons co-innervating the colon and the urinary bladder express ASIC-3. By contrast, extrinsic primary afferent neurons innervating the colon only or the urinary bladder only were positive for ASIC-3 in 39.3% and 42.6%, respectively. Echography-guided intravesical administration of acetic acid resulted in colonic hypersensitivity to colorectal distension. This effect started 1 h post-injection and lasted up to 24 h, and was not longer seen after 3 days after injection. No colonic hyperpermeability and no difference in urinary bladder and colon MPO activity was observed between control and acetic acid-treated rats. Colonic sensitization by intravesical acetic acid administration was prevented by S1 intrathecal administration of APETx2.ConclusionWe developed an acute pelvic cross-organ sensitization model in conscious rat. In this model, cross-organ sensitization is likely to involve S1-L6 extrinsic primary afferents co-innervating the colon and urinary bladder through an ASIC-3 pathway.

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Acid-sensing ion channel (ASIC) 1a/2a heteromers have a flexible 2:1/1:2 stoichiometry.

Publications

Acid-sensing ion channel (ASIC) 1a/2a heteromers have a flexible 2:1/1:2 stoichiometry.

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