title: Properties of ATP-gated ion channels assembled from P2X2 subunits in mouse cochlear Reissner's membrane epithelial cells.
abstract: In the cochlea, Reissner's membrane separates the scala media endolymphatic compartment that sustains the positive endocochlear potential and ion composition necessary for sound transduction, from the scala vestibuli perilymphatic compartment. It is known that with sustained elevated sound levels, adenosine 5'-triphosphate (ATP) is released into the endolymph and ATP-gated ion channels on the epithelial cells lining the endolymphatic compartment shunt the electrochemical driving force, contributing to protective purinergic hearing adaptation. This study characterises the properties of epithelial cell P2X(2)-type ATP-activated membrane conductance in the mouse Reissner's membrane, which forms a substantial fraction of the scale media surface. The cells were found to express two isoforms (a and b) of the P2X(2) subunit arising from alternative splicing of the messenger RNA (mRNA) transcript that could contribute to the trimeric subunit assembly. The ATP-activated conductance demonstrated both immediate and delayed desensitisation consistent with incorporation of the combination of P2X(2) subunit isoforms. Activation by the ATP analogue 2meSATP had equipotency to ATP, whereas α,β-meATP and adenosine 5'-diphosphate (ADP) were ineffective. Positive allosteric modulation of the P2X(2) channels by protons was profound. This native conductance was blocked by the P2X(2)-selective blocker pyridoxal-phosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) and the conductance was absent in these cells isolated from mice null for the P2rX2 gene encoding the P2X(2) receptor subunit. The activation and desensitisation properties of the Reissner's membrane epithelial cell ATP-gated P2X(2) channels likely contribute to the sensitivity and kinetics of purinergic control of the electrochemical driving force for sound transduction invoked by noise exposure.
authors.affiliation: Department of Physiology, University of Auckland, Auckland, New Zealand.
authors.forename: Rachel T
authors.initials: RT
authors.lastname: Morton-Jones
authors.affiliation: Department of Physiology, University of Auckland, Auckland, New Zealand.|Centre for Brain Research, School of Medical Sciences, University of Auckland, Auckland, New Zealand.
authors.forename: Srdjan M
authors.initials: SM
authors.lastname: Vlajkovic
authors.affiliation: Department of Physiology, University of Auckland, Auckland, New Zealand.|Centre for Brain Research, School of Medical Sciences, University of Auckland, Auckland, New Zealand.|Section of Audiology, School of Population Health, University of Auckland, Private Bag 92019, Auckland, New Zealand.
authors.forename: Peter R
authors.initials: PR
authors.lastname: Thorne
authors.affiliation: Boston Scientific, San Jose, CA, 95134, USA.
authors.forename: Debra A
authors.initials: DA
authors.lastname: Cockayne
authors.affiliation: Departments of Surgery and Neurosciences, VA Medical Center, University of California San Diego, La Jolla, CA, 92037, USA.
authors.forename: Allen F
authors.initials: AF
authors.lastname: Ryan
authors.affiliation: Translational Neuroscience Facility and Department of Physiology, School of Medical Sciences, UNSW Australia, Sydney, NSW, 2052, Australia. g.housley@unsw.edu.au.
authors.forename: Gary D
authors.identifier: http://orcid.org/0000-0002-8413-588X
authors.initials: GD
authors.lastname: Housley
mesh_terms: D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology / Q000502:physiology*; D000818:Animals; D003051:Cochlea / Q000378:metabolism*; D004847:Epithelial Cells / Q000378:metabolism*; D006309:Hearing; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D058920:Purinergic P2X Receptor Antagonists / Q000494:pharmacology; D011732:Pyridoxal Phosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D058476:Receptors, Purinergic P2X2 / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D013873:Thionucleotides / Q000494:pharmacology
chemical_list: D007473:Ion Channels; D058920:Purinergic P2X Receptor Antagonists; D012333:RNA, Messenger; D058476:Receptors, Purinergic P2X2; D013873:Thionucleotides; C077792:pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid; D011732:Pyridoxal Phosphate; D000255:Adenosine Triphosphate; C002630:alpha,beta-methyleneadenosine 5'-triphosphate; C008501:2-methylthio-ATP
keywords: ATP-gated ion channel; Cochlea; Desensitisation; Hearing; Knockout; Mouse; P2X receptor; P2rX2 gene; Purinergic receptor pharmacology; Splice variants