Tissue distribution and physiorogical function of ATP receptors

采用11种不同P2受体亚型特异性引物逆转录偶联多聚酶链反应（RT-PCR）检测中枢神经系统P2嘌呤受体mRNA的表达。在最佳条件下，发现P2X_4和P2X_6受体在大鼠脑中是优势的P2X嗜离子受体。P2X_7受体mRNA也普遍表达，但表达程度较低。P2X_2和P2X_5受体mrna分布更为离散，定位于中脑、脑干和脊髓。P2 X_3仅在脑干和脊髓中检测到。P2X_1在大鼠脑中表达较少。而G蛋白偶联P2Y受体亚型在脑内分布广泛，相对数量为P2Y_1≧P2Y_2≧P2Y_4>P2Y_6。在出生后发育过程中，P2X_2受体mRNA在许多脑区高表达，并在发育过程中逐渐降低。P2Y_2和P2Y_6受体增加。这些结果表明，几种P2受体在大鼠脑中以区域特异性和发育依赖性的方式表达。另一方面，在来自中枢神经系统的细胞系中发现了一种独特的atp诱导的反应，这种反应不适合任何克隆的P2受体。这种反应被确定为发生在膜表面微域的事件，细胞外ATP被外核苷酶快速定量地转化为腺苷，导致P1腺苷受体的激活。这种atp诱导的反应比腺苷诱导的反应更有效。因此，外核苷酸酶和P1受体紧密地定位于膜表面，并在功能上偶联以响应ATP。

P2 purinoceptor mRNA expression in the central nervous system was examined by the reverse transcription-coupled polymalase chain reaction (RT-PCR) with 11 different P2 receptor subtype-specific primers. Under an optimal condition, P2X_4 and P2X_6 receptors were found to be dominant P2X ionotropic receptors in rat brain. P2X_7 receptor mRNA was also ubiquitously expressed to a lesser extent. P2X_2 and P2X_5 receptor mRNAs exhibited more discrete distribution, localized in midbrain, brain stem and spinal cord. P2 X_3 was only detected in the brain stem and spinal cord. P2X_1 was little expressed in the rat brain. In contrast, G protein-coupled P2Y receptor subtypes were widely distributed in the brain and relative amount was P2Y_1≧P2Y_2≧P2Y_4>P2Y_6. During the postnatal development, P2X_2 receptor mRNA was highly expressed in many brain regions and progressively decreased during the development. In contrast, P2Y_2 and P2Y_6 receptors were increased. These results demonstrate that several P2 receptors were expressed in the rat brain in a region specific and development-dependent manner.On the other hand, a unique ATP-induced response that did not fit with any cloned P2 receptors was found in cell lines derived from the central nervous system. This response was identified as an event occurring in a membrane surface microdomain where extracellular ATP was rapidly and quantitatively converted into adenosine by ectonucleotidases, resulting in activation of P1 adenosine receptors. This ATP-induced response was somewhat more potent than adenosine-induced one. It is therefore suggested that ecto-nucleotidases and P1 receptors are closely localized in the membrane surface, and functionally couple to respond to ATP.