Choi O H, Lee J H, Kassessinoff T, Cunha-Melo J R, Jones S V, Beaven M A
Laboratory of Chemical Pharmacology, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892.
J Immunol. 1993 Nov 15;151(10):5586-95.
Because of unresolved questions about the mechanism of Ag-stimulated Ca2+ influx, Ca2+ mobilization in response to carbachol and Ag was compared in transfected rat basophilic RBL-2H3(ml) cells that expressed both Fc epsilon and ml muscarinic receptors. Although the stimulants activated phospholipase C via different coupling mechanisms, a G protein for carbachol or a tyrosine kinase for Ag, they released Ca2+ from the same intracellular pool and used the same or very similar mechanisms for influx of Ca2+ as indicated by the similar patterns of inhibition of uptake of 45Ca2+ by various cations. With both stimulants, influx and sustained increases in free cytosolic Ca2+ ([Ca2+]i) were associated with relatively small increases in inositol 1,4,5-trisphosphate (IP3). Blockade of Ca2+ influx resulted in rapid decline in [Ca2+]i to basal levels; resumption of influx caused a substantial "spike" in [Ca2+]i before [Ca2+]i reequilibrated at the same former steady-state levels but without perturbing levels of IP3. Thus, the refilling and discharge of Ca2+ from IP3-sensitive stores might occur synchronously on resumption of influx, or asynchronously during sustained influx and elevation of [Ca2+]i. Together, the results suggested that influx of Ca2+ in response to stimulation via Fc epsilon receptors occurred through a pathway, analogous to that observed with other types of stimulants, in which Ca2+ influx follows emptying of intracellular Ca2+ stores by IP3. Also, secretion was highly dependent on this IP3-dependent pathway.
由于关于抗原刺激的钙离子内流机制的问题尚未解决，因此在同时表达Fcε和m1毒蕈碱受体的转染大鼠嗜碱性RBL-2H3(ml)细胞中，比较了对卡巴胆碱和抗原的钙离子动员情况。尽管刺激物通过不同的偶联机制激活磷脂酶C，卡巴胆碱通过G蛋白，抗原通过酪氨酸激酶，但它们从相同的细胞内池释放钙离子，并且如各种阳离子对45Ca2+摄取的抑制模式相似所示，它们利用相同或非常相似的机制进行钙离子内流。对于这两种刺激物，钙离子内流和游离胞质钙离子（[Ca2+]i）的持续增加都与肌醇1,4,5-三磷酸（IP3）的相对较小增加有关。钙离子内流的阻断导致[Ca2+]i迅速下降至基础水平；内流的恢复导致[Ca2+]i出现大幅“峰值”，然后[Ca2+]i在相同的先前稳态水平重新平衡，但不影响IP3水平。因此，在钙离子内流恢复时，IP3敏感储存库中钙离子的再填充和释放可能同步发生，或者在钙离子持续内流和[Ca2+]i升高期间异步发生。总之，这些结果表明，通过Fcε受体刺激引起的钙离子内流是通过一条类似于其他类型刺激物所观察到的途径发生的，即钙离子内流跟随IP3使细胞内钙离子储存库排空之后。此外，分泌高度依赖于这条依赖IP3的途径。
