Oregon Hearing Research Center, NRC04, Oregon Health & Science Univ., 3181 S.W. Sam Jackson Park Rd., Portland, OR 97239, USA.
Am J Physiol Heart Circ Physiol. 2011 Jul;301(1):H69-78. doi: 10.1152/ajpheart.01035.2010. Epub 2011 Apr 1.
The cochlear lateral wall generates the endocochlear potential (EP), which creates a driving force for the hair cell transduction current and is essential for normal hearing. Blood flow at the cochlear lateral wall is critically important for maintaining the EP. The vulnerability of the EP to hypoxia suggests that the blood flow in the cochlear lateral wall is dynamically and precisely regulated to meet the changing metabolic needs of the cochlear lateral wall. It has been reported that ATP, an important extracellular signaling molecule, plays an essential role in regulating cochlear blood flow. However, the cellular mechanism underlying ATP-induced regional blood flow changes has not been investigated. In the current study, we demonstrate that 1) the P2X4 receptor is expressed in endothelial cells (ECs) of spiral ligament (SL) capillaries. 2) ATP elicits a characteristic current through P2X4 on ECs in a dose-dependent manner (EC(50) = 0.16 mM). The ATP current has a reversal potential at ∼0 mV; is inhibited by 5-(3-bromophenyl)-1,3-dihydro-2H-benzofuro[3,2-e]-1,4-diazepin-2-one (5-BDBD), LaCl(3), pyridoxal phosphate-6-azo(benzene-2,4-disulfonic acid) tetrasodium salt hydrate (PPADS), and extracellular acidosis; and is less sensitive to α,β-methyleneadenosine 5'-triphosphate (α,β-MeATP) and 2'- and 3'-O-(4-benzoyl-benzoyl) adenosine 5'-triphosphate (BzATP). 3) ATP elicits a transient increase of intracellular Ca(2+) in ECs. 4) In accordance with the above in vitro findings, perilymphatic ATP (1 mM) caused dilation in SL capillaries in vivo by 11.5%. N(ω)-nitro-l-arginine methyl ester hydrochloride (l-NAME), a nonselective inhibitor of nitric oxide synthase, or 5-BDBD, the specific P2X4 inhibitor, significantly blocked the dilation. These findings support our hypothesis that extracellular ATP regulates cochlear lateral blood flow through P2X4 activation in ECs.
耳蜗外侧壁产生内淋巴液（EP），为毛细胞转导电流提供驱动力，对正常听力至关重要。耳蜗外侧壁的血流对于维持 EP 至关重要。EP 对缺氧的敏感性表明，耳蜗外侧壁的血流受到动态和精确的调节，以满足耳蜗外侧壁不断变化的代谢需求。有报道称，ATP 作为一种重要的细胞外信号分子，在调节耳蜗血流方面发挥着重要作用。然而，ATP 诱导局部血流变化的细胞机制尚未得到研究。在本研究中，我们证明了：1）P2X4 受体在螺旋韧带（SL）毛细血管的内皮细胞（ECs）中表达。2）ATP 通过 EC 上的 P2X4 以剂量依赖性方式引起特征性电流（EC50=0.16 mM）。ATP 电流的反转电位约为 0 mV；被 5-(3-溴苯基)-1,3-二氢-2H-苯并呋[3,2-e]-1,4-二氮杂卓-2-酮（5-BDBD）、LaCl3、吡啶醛磷酸盐-6-偶氮（苯-2,4-二磺酸）四钠盐水合物（PPADS）和细胞外酸中毒抑制；并且对α,β-亚甲基腺苷 5'-三磷酸（α,β-MeATP）和 2'-和 3'-O-(4-苯甲酰苯甲酰)腺苷 5'-三磷酸（BzATP）的敏感性较低。3）ATP 在 ECs 中引起细胞内 Ca2+的短暂增加。4）根据上述体外发现，在体Perilymph 中的 ATP（1 mM）引起 SL 毛细血管扩张 11.5%。N(ω)-硝基-L-精氨酸甲酯盐酸盐（l-NAME），一种非选择性一氧化氮合酶抑制剂，或 5-BDBD，特异性 P2X4 抑制剂，显著阻断了扩张。这些发现支持我们的假设，即细胞外 ATP 通过 EC 上的 P2X4 激活来调节耳蜗外侧血流。
