Section on Cellular Signaling, Endocrinology and Reproduction Research Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, USA.
Purinergic Signal. 2005 Jun;1(2):135-44. doi: 10.1007/s11302-005-6208-y. Epub 2005 Mar 7.
Hypothalamic and pituitary cells express G protein-coupled adenosine and P2Y receptors and cation-conducting P2X receptor-channels, suggesting that extracellular ATP and other nucleotides may function as autocrine and/or paracrine signaling factors in these cells. Consistent with this hypothesis, we show that cultured normal and immortalized pituitary and hypothalamic cells release ATP under resting conditions. RT-PCR analysis also revealed the presence of transcripts for ecto-nucleotidase eNTPDase 1-3 in these cells. These enzymes were functional as documented by degradation of endogenously released and exogenously added ATP. Blocking the activity of eNTPDases by ARL67156 led to an increase in ATP release in perifused pituitary cells and inhibition of degradation of extracellularly added ATP. Furthermore, the addition of apyrase, a soluble ecto-nucleotidase, and the expression of recombinant mouse eNTPDase-2, enhanced degradation of both endogenously released and exogenously added ATP. The released ATP by resting hypothalamic cells was sufficient to activate and desensitize high-affinity recombinant P2X receptors, whereas facilitation of ATP metabolism by the addition of apyrase protected their desensitization. These results indicate that colocalization of ATP release sites and ecto-nucleotidase activity at the plasma membrane of hypothalamic and pituitary cells provides an effective mechanism for the operation of nucleotides as extracellular signaling molecules.
下丘脑和垂体细胞表达 G 蛋白偶联的腺苷和 P2Y 受体以及阳离子传导的 P2X 受体通道，这表明细胞外 ATP 和其他核苷酸可能作为这些细胞的自分泌和/或旁分泌信号因子发挥作用。与这一假说一致，我们表明培养的正常和永生化的垂体和下丘脑细胞在静息状态下释放 ATP。RT-PCR 分析还显示这些细胞存在外核苷酸酶 eNTPDase 1-3 的转录本。这些酶具有功能，如内源性释放和外源性添加的 ATP 的降解所证明的那样。通过 ARL67156 阻断 eNTPDases 的活性导致灌流的垂体细胞中 ATP 释放增加，并抑制细胞外添加的 ATP 的降解。此外，添加溶解的外核苷酸酶 apyrase 和表达重组小鼠 eNTPDase-2，增强了内源性释放和外源性添加的 ATP 的降解。静息下丘脑细胞释放的 ATP 足以激活和脱敏高亲和力重组 P2X 受体，而添加 apyrase 促进 ATP 代谢则保护其脱敏。这些结果表明，下丘脑和垂体细胞的质膜上 ATP 释放位点和外核苷酸酶活性的共定位为核苷酸作为细胞外信号分子的作用提供了一种有效的机制。
