Kelley L L, Blackmore P F, Graber S E, Stewart S J
Department of Pathology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232.
J Biol Chem. 1990 Oct 15;265(29):17657-64.
Prostaglandins (PGs) of the E series are recognized by specific receptors on T lymphocytes which lead to an increase in cAMP. The role of cAMP in modulation of T lymphocyte function is unknown. Here, we demonstrate that agents which increase cAMP in human T cells raise the intracellular free calcium concentration ([Ca2+]i). This increase in [Ca2+]i occurred following receptor stimulation with PGEs or by bypassing the receptor with the cell-permeant analog 8-(4-chlorophenylthio)-cAMP or forskolin, a direct activator of adenylyl cyclase. The calcium response to a submaximally stimulatory concentration of PGE2 was potentiated by the cAMP phosphodiesterase inhibitor isobutylmethylxanthine. A time course of cAMP production in response to PGE2 stimulation closely resembled the calcium response and suggested that the two events were coincident. The PGE2 concentrations required to achieve 50% maximum effect of cAMP production and increases in [Ca2+]i were similar, 0.07 and 0.15 microM respectively. Chelation of extracellular Ca2+ did not abolish the PGE2-stimulated Ca2+ response, suggesting that an intracellular source of calcium was sensitive to cAMP. Significant inositol phosphate production was not detected in response to PGE2 over a wide concentration range. The PGE2-induced calcium response curves were of lesser magnitude with shorter times to peak than those of a known inositol 1,4,5 trisphosphate-producing agonist, anti-CD3, suggesting distinct Ca2+ release mechanisms. However, the cAMP-releasable store appeared to be contained within the inositol trisphosphate-releasable store since no response could be seen with cAMP-elevating agents following emptying of the inositol trisphosphate-sensitive pool of Ca2+.
E系列前列腺素（PGs）可被T淋巴细胞上的特异性受体识别，这些受体可导致环磷酸腺苷（cAMP）增加。cAMP在调节T淋巴细胞功能中的作用尚不清楚。在此，我们证明，能增加人T细胞中cAMP的药物会提高细胞内游离钙浓度（[Ca2+]i）。在用前列腺素E（PGEs）刺激受体后，或通过使用细胞渗透性类似物8-（4-氯苯基硫代）-cAMP或福斯可林（一种腺苷酸环化酶的直接激活剂）绕过受体后，[Ca2+]i会出现这种增加。cAMP磷酸二酯酶抑制剂异丁基甲基黄嘌呤可增强对亚最大刺激浓度的PGE2的钙反应。对PGE2刺激的cAMP产生的时间进程与钙反应非常相似，表明这两个事件是同时发生的。达到cAMP产生最大效应的50%和[Ca2+]i增加所需的PGE2浓度相似，分别为0.07和0.15微摩尔。细胞外Ca2+的螯合并未消除PGE2刺激的Ca2+反应，这表明细胞内钙源对cAMP敏感。在很宽的浓度范围内，未检测到对PGE2有显著的肌醇磷酸产生。PGE2诱导的钙反应曲线的幅度较小，达到峰值的时间比已知的产生肌醇1,4,5-三磷酸的激动剂抗CD3的曲线短，这表明存在不同的Ca2+释放机制。然而，cAMP可释放的储存库似乎包含在肌醇三磷酸可释放的储存库中，因为在排空肌醇三磷酸敏感的Ca2+池后，用提高cAMP的药物看不到反应。
