Koshimizu T A, Tomić M, Wong A O, Zivadinovic D, Stojilkovic S S
Endocrinology and Reproduction Research Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-4510, USA.
Endocrinology. 2000 Nov;141(11):4091-9. doi: 10.1210/endo.141.11.7737.
Purinergic G protein-coupled receptors (P2YR) and ion-conducting receptor-channels (P2XR) are present in the pituitary. However, their identification, expression within pituitary cell subpopulations, and the ability to elevate intracellular Ca2+ concentration ([Ca2+]i) in response to ATP stimulation were incompletely characterized. Here we show that mixed populations of rat anterior pituitary cells express messenger RNA transcripts for P2Y2R, P2X2aR, P2X2bR, P2X3R, P2X4R, and P2X7R. The transcripts and functional P2Y2R were identified in lactotrophs and GH3 cells, but not in somatotrophs and gonadotrophs, and their activation by ATP led to an extracellular Ca2+-independent rise in [Ca2+]i in about 40% of cells tested. Lactotrophs and GH3 cells, but not somatotrophs, also express transcripts for P2X7R, P2X3R, and P2X4R. Functional P2X7R were identified in 74% of lactotrophs, whereas 50% of these cells expressed P2X3R and 33% expressed P2X4R. Coexpression of these receptor subtypes in single lactotrophs was frequently observed. Purified somatotrophs expressed transcripts for P2X2aR and P2X2bR, and functional receptors were identified in somatotrophs and gonadotrophs, but not in lactotrophs. Consistent with the cell-specific expression of transcripts for P2X2R and P2X3R, the expression of their functional heteromers was not evident in pituitary cells. Receptors differed in their capacities to elevate and sustain Ca2+ influx-dependent rise in [Ca2+]i during the prolonged ATP stimulation. These results indicate that the purinergic system of anterior pituitary is extremely complex and provides an effective mechanism for generating a cell- and receptor-specific Ca2+ signaling pattern in response to a common agonist.
嘌呤能G蛋白偶联受体（P2YR）和离子传导受体通道（P2XR）存在于垂体中。然而，它们的鉴定、在垂体细胞亚群中的表达以及对ATP刺激作出反应时升高细胞内Ca2+浓度（[Ca2+]i）的能力尚未得到充分表征。在此，我们表明大鼠垂体前叶细胞混合群体表达P2Y2R、P2X2aR、P2X2bR、P2X3R、P2X4R和P2X7R的信使RNA转录本。在催乳素细胞和GH3细胞中鉴定出了转录本和功能性P2Y2R，但在生长激素细胞和促性腺激素细胞中未鉴定出，并且它们被ATP激活导致在约40%的测试细胞中细胞外Ca2+非依赖性的[Ca2+]i升高。催乳素细胞和GH3细胞而非生长激素细胞也表达P2X7R、P2X3R和P2X4R的转录本。在74%的催乳素细胞中鉴定出功能性P2X7R，而这些细胞中有50%表达P2X3R，33%表达P2X4R。经常观察到这些受体亚型在单个催乳素细胞中共表达。纯化的生长激素细胞表达P2X2aR和P2X2bR的转录本，并且在生长激素细胞和促性腺激素细胞中鉴定出功能性受体，但在催乳素细胞中未鉴定出。与P2X2R和P2X3R转录本的细胞特异性表达一致，它们功能性异聚体的表达在垂体细胞中不明显。在长时间的ATP刺激期间，受体在升高和维持Ca2+流入依赖性的[Ca2+]i升高的能力方面存在差异。这些结果表明垂体前叶的嘌呤能系统极其复杂，并提供了一种有效的机制，以响应共同的激动剂产生细胞和受体特异性的Ca2+信号模式。
