Maeyama K, Hohman R J, Ali H, Cunha-Melo J R, Beaven M A
Laboratory of Chemical Pharmacology, National Heart, Lung, and Blood Institute, Bethesda, MD 20982.
J Immunol. 1988 Jun 1;140(11):3919-27.
Previous studies have shown that hydrolysis of membrane inositol phospholipids in rat basophilic leukemia (RBL-2H3) cells depended on the rate and extent of the aggregation of receptors of IgE. This response was used as an experimental probe to study the role of IgE receptors in initiating stimulatory and inhibitory processes within the cell. The response was amplified markedly by increasing the concentration of external Ca2+ from 0 to 1 mM, but the concentration required to support half-maximal response varied from less than 0.1 mM for the most potent cross-linking reagent, DNP24BSA (24 molecules of DNP attached to 1 molecule of BSA) to 0.5 mM for the least potent reagent, aggregated OVA. The dependency of phosphoinositide hydrolysis on external Ca2+ was reduced to zero once hydrolysis of inositol phospholipids was underway but secretion of histamine remained totally dependent on the presence of 0.5 to 1 mM external Ca2+. The stimulatory response persisted as long as receptors remained aggregated but it was modulated by a biochemical process, possibly the activation of protein kinase C, that targeted specifically aggregated receptors, or an associated protein. For example, when cells had become desensitized to high concentrations of one Ag, a normal response could be evoked with a second Ag. Also cells that had become desensitized could be reactivated by permeabilizing the cells. Interestingly, bell-shaped Ag dose-response curves, which were characteristic for both the phosphoinositide and secretory responses, were transformed to sigmoid-shaped curves once cells were permeabilized and dialyzed.
先前的研究表明，大鼠嗜碱性白血病（RBL-2H3）细胞中膜肌醇磷脂的水解取决于IgE受体聚集的速率和程度。这种反应被用作实验探针，以研究IgE受体在启动细胞内刺激和抑制过程中的作用。通过将细胞外Ca2+浓度从0增加到1 mM，该反应得到显著放大，但支持半数最大反应所需的浓度因交联剂的效力不同而有所变化，对于最有效的交联剂DNP24BSA（24个DNP分子连接到1个BSA分子），该浓度小于0.1 mM，而对于效力最低的试剂——聚集的OVA，该浓度为0.5 mM。一旦肌醇磷脂开始水解，磷酸肌醇水解对细胞外Ca2+的依赖性就会降至零，但组胺的分泌仍然完全依赖于0.5至1 mM细胞外Ca2+的存在。只要受体保持聚集状态，刺激反应就会持续存在，但它会受到一个生化过程的调节，这个过程可能是蛋白激酶C的激活，该激酶特异性地作用于聚集的受体或相关蛋白。例如，当细胞对高浓度的一种抗原脱敏后，用第二种抗原仍可引发正常反应。而且，已经脱敏的细胞可以通过使其透化而重新激活。有趣的是，磷酸肌醇和分泌反应所特有的钟形抗原剂量反应曲线，在细胞透化和透析后会转变为S形曲线。
