title: Ecto-nucleotidases terminate purinergic signalling in the cochlear endolymphatic compartment.
abstract: There is strong evidence for a purinergic signalling system in the inner ear which regulates auditory sensitivity. This study describes the terminating mechanism for purinergic signalling in the cochlear endolymphatic compartment via ecto-nucleotidases. Exogenous ATP was introduced into the scala media (SM) of the isolated, perfused guinea-pig cochlea, and the effluent was assayed for the adenine nucleotide metabolites by reverse-phase HPLC. Tissue viability was confirmed by fluorescence imaging of cochlear tissues. Extracellular ATP degradation to adenosine was Ca2+/Mg2+ dependent, and was not affected by inhibitors of intracellular ATPases and non-specific alkaline phosphatase. High azide concentration (5 mM) and suramin produced an inhibitory effect on ATP hydrolysis, consistent with inhibition of E-type ATPase activity. The Vmax of ATP hydrolysis (2564 mumol min-1 SM-1) was indicative of high ecto-ATPase activity. Our results support the role of ecto-nucleotidases as a principal mechanism for termination of purinergic signalling within SM, a compartment of the cochlea showing considerable P2X receptor expression.
authors.affiliation: Department of Physiology, University of Auckland, New Zealand.
authors.forename: S M
authors.initials: SM
authors.lastname: Vlajkovic
authors.forename: P R
authors.initials: PR
authors.lastname: Thorne
authors.forename: G D
authors.initials: GD
authors.lastname: Housley
authors.forename: D J
authors.initials: DJ
authors.lastname: Muñoz
authors.forename: I S
authors.initials: IS
authors.lastname: Kendrick
mesh_terms: D000241:Adenosine / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D002470:Cell Survival; D003051:Cochlea / Q000166:cytology / Q000201:enzymology / Q000502:physiology*; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008208:Lymphatic System / Q000502:physiology*; D008297:Male; D010477:Perfusion; D018048:Receptors, Purinergic P2 / Q000096:biosynthesis / Q000502:physiology*; D015398:Signal Transduction; D013498:Suramin / Q000494:pharmacology
chemical_list: D018048:Receptors, Purinergic P2; D013498:Suramin; D000255:Adenosine Triphosphate; D000469:Alkaline Phosphatase; D000251:Adenosine Triphosphatases; D017301:Ca(2+) Mg(2+)-ATPase; C027201:ectoATPase; D000241:Adenosine