Vlajkovic S M, Thorne P R, Housley G D, Muñoz D J, Kendrick I S
Department of Physiology, University of Auckland, New Zealand.
Neuroreport. 1998 May 11;9(7):1559-65.
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.
有充分证据表明内耳存在嘌呤能信号系统，该系统可调节听觉敏感性。本研究描述了通过胞外核苷酸酶在内耳内淋巴腔室中嘌呤能信号的终止机制。将外源性ATP引入离体灌注豚鼠耳蜗的中阶（SM），并通过反相高效液相色谱法分析流出物中的腺嘌呤核苷酸代谢产物。通过耳蜗组织的荧光成像确认组织活力。细胞外ATP降解为腺苷是Ca2+/Mg2+依赖性的，不受细胞内ATP酶抑制剂和非特异性碱性磷酸酶的影响。高叠氮化物浓度（5 mM）和苏拉明对ATP水解产生抑制作用，这与E型ATP酶活性的抑制一致。ATP水解的Vmax（2564 μmol min-1 SM-1）表明胞外ATP酶活性较高。我们的结果支持胞外核苷酸酶作为终止中阶内嘌呤能信号的主要机制的作用，中阶是耳蜗中显示大量P2X受体表达的腔室。
