Carew M A, Wu M L, Law G J, Tseng Y Z, Mason W T
Department of Neurobiology, Babraham Institute, Cambridge, UK.
Cell Calcium. 1994 Sep;16(3):227-35. doi: 10.1016/0143-4160(94)90025-6.
Extracellular ATP has been previously shown to activate calcium signalling in pituitary cell populations [1] but the particular cell types involved have not been identified. We used video imaging of Fura-2 loaded into single rat pituitary cells and identified as lactotrophs to study the effects of extracellular ATP on [Ca2+]i. ATP does not permeabilize the cells as shown by exclusion of propidium iodide. ATP causes two types of calcium transients in lactotrophs. The most common response is a rapid increase in [Ca2+]i that decays slowly and is terminated by washout of ATP. This type of response is also seen in calcium-free medium, demonstrating mobilization of calcium stores dependent upon the presence of the agonist. ATP also stimulates calcium entry as detected by Mn(2+)-quenching of Fura-2. ATP in Mg(2+)-free medium and ATP gamma S are effective agonists suggesting ATP4- is the active form. The presence of P2-purinoceptors is apparent because ATP, ADP and AMP increase [Ca2+]i in decreasing order of potency and adenosine has no effect. ATP-induced calcium transients are reduced by the P2-purinoceptor antagonists suramin and quinidine. UTP is equipotent with ATP and defines the receptor subtype as P2U. We conclude that ATP4- acts on rat lactotrophs via P2U-purinoceptors to elevate [Ca2+]i from intracellular and extracellular sources.
先前的研究表明，细胞外ATP可激活垂体细胞群中的钙信号传导[1]，但尚未确定具体涉及的细胞类型。我们利用装载有Fura-2的单个大鼠垂体细胞的视频成像技术，并将其鉴定为催乳素细胞，以研究细胞外ATP对细胞内钙离子浓度（[Ca2+]i）的影响。碘化丙啶排斥实验表明，ATP不会使细胞透化。ATP在催乳素细胞中引发两种类型的钙瞬变。最常见的反应是[Ca2+]i迅速升高，随后缓慢衰减，并通过洗脱ATP而终止。在无钙培养基中也观察到这种类型的反应，表明钙库的动员依赖于激动剂的存在。通过Fura-2的锰（2+）猝灭检测到，ATP还能刺激钙内流。无镁培养基中的ATP和ATPγS是有效的激动剂，表明ATP4-是活性形式。P2嘌呤受体的存在很明显，因为ATP、ADP和AMP以效力递减的顺序增加[Ca2+]i，而腺苷则无作用。ATP诱导的钙瞬变可被P2嘌呤受体拮抗剂苏拉明和奎尼丁降低。UTP与ATP等效，确定受体亚型为P2U。我们得出结论，ATP4-通过P2U嘌呤受体作用于大鼠催乳素细胞，从细胞内和细胞外来源升高[Ca2+]i。
