Distribution of ectonucleoside triphosphate diphosphohydrolases 1 and 2 in rat cochlea Srdjan M. Vlajkovic a;b;  , Peter R. Thorne a;b , Jean Se ¤vigny c , Simon C. Robson d , Gary D. Housley a a Division of Physiology, Faculty of Medical and Health Sciences, The University of Auckland, Private Bag 92019, Auckland, New Zealand b Discipline of Audiology, Faculty of Medical and Health Sciences, The University of Auckland, Private Bag 92019, Auckland, New Zealand c Centre de Recherche en Rhumatologie et Immunologie, CHUQ, Universite ¤ Laval, Sainte-Foy, QC, Canada d Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA Received 20 December 2001; accepted 9 April 2002 Abstract Extracellular ATP and other extracellular nucleotides acting via P2 receptors in the inner ear initiate a wide variety of signalling pathways important for regulation of hearing and balance. Ectonucleotidases are extracellular nucleotide-metabolising enzymes that modulate purinergic signalling in most tissues. Major ectonucleotidases in the cochlea are likely members of the ectonucleoside triphosphate diphosphohydrolase (E-NTPDase) family. In this study, we provide a detailed description of NTPDase1 and NTPDase2 distribution in cochlear tissues using immunocytochemistry. E-NTPDase immunoreactivity was not equally distributed in the tissues bordering scala media. It was observed in the organ of Corti, including sensory and supporting cells, but was notably absent from Reissner’s membrane and most of the marginal cells of the stria vascularis. NTPDase1 expression was most prominent in the cochlear vasculature and cell bodies of the spiral ganglion neurones, whereas considerable NTPDase2 immunoreactivity was detected in the stria vascularis. Both E-NTPDases were expressed in the cuticular plates of the sensory hair cells and nerve fibres projecting from the synaptic area underneath the inner and outer hair cells. E-NTPDase localisation corresponds to the reported distribution of some P2X receptor subunits (P2X 2 in particular) in sensory, supporting and neural cells and also P2Y receptor distribution in the vasculature and secretory tissues of the lateral wall. The role for E-NTPDases in purinergic signalling is most likely to regulate extracellular nucleoside triphosphate and diphosphate levels and thus provide termination for extracellular ATP signalling that has been linked to control of cochlear blood flow, electrochemical regulation of sound transduction and to neurotransmission in the cochlea. ß 2002 Elsevier Science B.V. All rights reserved. Key words: Ectonucleoside triphosphate diphosphohydrolase; Ectonucleotidase; ATP; P2 receptor; Cochlea; Immunohistochemistry 1. Introduction Extracellular nucleotides such as ATP, ADP, UTP, UDP and diadenosine polyphosphates act as signalling molecules to in£uence cellular function in most tissues. Extracellular nucleotides are involved in short-term sig- nalling, such as neurotransmission, secretion and vaso- dilation, and in long-term trophic signalling including processes involved in development, regeneration, cell proliferation and death (Burnstock, 2001). Signal trans- mission occurs via fast P2X receptors (ATP-gated cat- ion channels) and slower P2Y receptors (G protein- coupled receptors) (Abbracchio and Burnstock, 1998). 0378-5955 / 02 / $ ^ see front matter ß 2002 Elsevier Science B.V. All rights reserved. PII:S0378-5955(02)00460-4 * Corresponding author. Tel.: +64 (9) 3737599; Fax: +64 (9) 3737499. E-mail address: s.vlajkovic@auckland.ac.nz (S.M. Vlajkovic). Abbreviations: bc, basal cell; bm, basilar membrane; bv, blood vessel; cc, Claudius’ cell; dc, Deiters’ cell; hc, Hensen’s cells; ibc, inner border cell; ic, intermediate cell; igsb, intraganglionic spiral bundle; ihc, inner hair cell; ipc, inner pillar cell; is, inner sulcus; isp, inner spiral plexus; lim, spiral limbus; mc, marginal cell; oc, organ of Corti; ohc, outer hair cell; os, outer sulcus; osb, outer spiral bundle; osl, osseous spiral lamina; opc, outer pillar cell; rl, reticular lamina; rm, Reissner’s membrane; sgn, spiral ganglion neurones; sl, spiral ligament; sp, spiral prominence; sr, synaptic region; sv, stria vascularis; tc, tunnel of Corti; tm, tectorial membrane Hearing Research 170 (2002) 127^138 www.elsevier.com/locate/heares