Botana L M, MacGlashan D W
Johns Hopkins Asthma and Allergy Center, Baltimore, Maryland 21224.
J Leukoc Biol. 1994 Jun;55(6):798-804. doi: 10.1002/jlb.55.6.798.
Drugs that elevate cAMP levels in human basophils are known to inhibit immunoglobulin E (IgE)-mediated histamine release. We have examined whether cAMP-active agents inhibit the cytosolic Ca2+, [Ca2+]i, response that normally accompanies activation of basophils. As previously described, this [Ca2+]i response is biphasic, one phase dependent on internal sources of calcium and a second later phase dependent on extracellular calcium, as observed in many cell types. Forskolin and rolipram or their combination had no effect on the initial elevation of cytosolic calcium that follows stimulation with anti-IgE antibody. In contrast, the second phase of the IgE-mediated calcium response was inhibited by these agents. For IgE-mediated responses, the relative efficacy of various cAMP active agents (rolipram approximately forskolin < dibutyryl cAMP < forskolin + rolipram) for the inhibition of histamine release and the second-phase calcium response was similar and roughly paralleled the measured increase in basophil cAMP. In contrast, neither the first nor the second phase of the f-Met-Leu-Phe (fMLP)-induced calcium response was inhibited by any of the cAMP-active agents tested. Indeed, at low concentrations of fMLP, a combination of forskolin and rolipram caused slight enhancement of the calcium response. This result was consistent with the observations that these agents had no effect or caused slight enhancement of histamine or leukotriene released induced by fMLP. Similarly, cAMP-active agents caused no inhibition of C5a or phorbol ester (phorbol myristate acetate)-induced histamine release. These observations suggest that inhibition of the phase of the calcium response that is dependent on extracellular calcium could account for the inhibition of histamine release by these agents. However, these studies also suggested that (1) this is effect is not exerted at the level of the inositol trisphosphate (InsP3) receptor or InsP3 metabolism and (2) the mechanisms that maintain the second-phase calcium response are possibly distinct for IgE- and fMLP-mediated reactions because cAMP-active agents inhibited the second-phase response of only one stimulus.
已知能提高人嗜碱性粒细胞中环磷酸腺苷（cAMP）水平的药物可抑制免疫球蛋白E（IgE）介导的组胺释放。我们研究了cAMP活性药物是否能抑制嗜碱性粒细胞激活时通常伴随的胞质钙离子（[Ca2+]i）反应。如前所述，这种[Ca2+]i反应是双相的，一个阶段依赖于钙的内部来源，第二个较晚的阶段依赖于细胞外钙，这在许多细胞类型中都有观察到。福斯可林和咯利普兰或它们的组合对用抗IgE抗体刺激后胞质钙的初始升高没有影响。相反，这些药物抑制了IgE介导的钙反应的第二阶段。对于IgE介导的反应，各种cAMP活性药物（咯利普兰≈福斯可林<二丁酰cAMP<福斯可林+咯利普兰）抑制组胺释放和第二阶段钙反应的相对效力相似，并且大致与测得的嗜碱性粒细胞cAMP增加平行。相比之下，测试的任何一种cAMP活性药物都没有抑制甲酰甲硫氨酸-亮氨酸-苯丙氨酸（f-Met-Leu-Phe，fMLP）诱导的钙反应的第一阶段或第二阶段。事实上，在低浓度的fMLP下，福斯可林和咯利普兰的组合导致钙反应略有增强。这一结果与这些药物对fMLP诱导释放的组胺或白三烯没有影响或略有增强的观察结果一致。同样，cAMP活性药物也没有抑制C5a或佛波酯（佛波醇肉豆蔻酸酯乙酸酯）诱导的组胺释放。这些观察结果表明，抑制依赖于细胞外钙的钙反应阶段可能是这些药物抑制组胺释放的原因。然而，这些研究还表明：（1）这种作用不是在肌醇三磷酸（InsP3）受体或InsP3代谢水平上发挥的；（2）维持第二阶段钙反应的机制可能因IgE和fMLP介导的反应而不同，因为cAMP活性药物仅抑制了一种刺激的第二阶段反应。
