Opiate receptor down-regulation and desensitization in neuroblastoma X glioma NG108-15 hybrid cells are two separate cellular adaptation processes.
Opiate receptor down-regulation and desensitization in neuroblastoma X glioma NG108-15 hybrid cells are two separate cellular adaptation processes.
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发表时间：
1983-11
影响因子：
3.6
通讯作者：
P. Law;D. Hom;H. Loh
中科院分区：
文献类型：
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作者：
P. Law;D. Hom;H. Loh
用阿片激动剂埃托啡对神经母细胞瘤 X 神经胶质瘤 NG108-15 杂交细胞进行长期治疗，导致阿片受体密度下降（受体下调）和阿片抑制前列腺素 E1 (PGE1) 刺激的环 AMP 水平增加的能力（受体脱敏）。阿片受体下调和脱敏是同源的，毒蕈碱、α2-肾上腺素能和 PGE1 受体结合没有明显变化，并且在埃托啡治疗 24 小时后，卡巴胆碱和去甲肾上腺素抑制 PGE1 刺激的环 AMP 水平增加的能力保留（尽管是调节）。 PGE1 刺激的环 AMP 水平增加在埃托啡处理的细胞和对照细胞中保持相同。多项证据表明 NG108-15 细胞中的受体脱敏和受体下调是两个独立的细胞适应过程。 (a) 对于似乎有效偶联的激动剂，即表观 Kd 值远大于其调节环 AMP 水平 (Ki) 的表观 IC50 值的激动剂，产生半最大下调所需的配体浓度与其 Ki 值类似，而产生半最大脱敏所需的配体浓度与其 Kd 值相关； (b) 受体脱敏先于受体下调； (c) 只有阿片激动剂可以产生受体下调，而阿片激动剂和部分激动剂都可以使受体后占据事件脱敏。通过将 NG108-15 细胞与埃托啡在 30 度下孵育 2 小时，获得了这些过程可解离性的进一步证据。在这些条件下，埃托啡调节腺苷酸环化酶的能力下降，而[3H]二丙诺啡结合保持不变。埃托啡处理 90 分钟后，D-Ala2-D-Leu5-脑啡肽竞争 [3H]二丙诺啡与完整细胞结合的 IC50 值增加了 19.6 倍，而纳洛酮 IC50 值保持不变。当在从长期用埃托啡处理的细胞分离的膜中进行受体结合时，IC50值的这种明显增加要低得多，大约是2倍。此外，在 10 mM Mg2+ 存在下对[3H]埃托啡与此类膜的结合分析表明，受体结合位点丢失，而表观亲和力没有变化，而[3H]二丙诺啡结合表明 Bmax 或 Kd 值没有显着变化。因此，在阿片受体脱敏过程中，激动剂高亲和力位点减少，受体总数没有明显变化。
Chronic treatment of neuroblastoma X glioma NG108-15 hybrid cells with the opiate agonist etorphine resulted in a decrease in both opiate receptor density (receptor down-regulation) and opiate ability to inhibit prostaglandin E1 (PGE1)-stimulated increases in cyclic AMP levels (receptor desensitization). Opiate receptor down-regulation and desensitization were homologous as indicated by the lack of apparent change in muscarinic, alpha 2-adrenergic, and PGE1 receptor binding and also retention, albeit modulation, of the ability of carbachol and norepinephrine to inhibit PGE1-stimulated increases in cyclic AMP levels after 24 hr of etorphine treatment. PGE1-stimulated increases in cyclic AMP levels remained identical in etorphine-treated and control cells. Several lines of evidence indicate that receptor desensitization and receptor down-regulation in NG108-15 cells are two separate cellular adaptation processes. (a) With an agonist which appears to be efficiently coupled, i.e., an agonist whose apparent Kd value is much larger than its apparent IC50 value for regulation of cyclic AMP levels (Ki), the concentration of ligand required to produce half-maximal down-regulation is analogous to its Ki value, whereas the concentration of ligand required to produce half-maximal desensitization is related to its Kd value; (b) receptor desensitization precedes receptor down-regulation; (c) only opiate agonists could produce receptor down-regulation, whereas both opiate agonists and partial agonists could desensitize post-receptor occupancy events. Still further evidence for dissociability of these processes was obtained by incubating NG108-15 cells with etorphine at 30 degrees for 2 hr. Under these conditions, there was a decrease in etorphine's ability to regulate adenylate cyclase while [3H]diprenorphine binding remained unaltered. IC50 values of D-Ala2-D-Leu5-enkephalin's competition for [3H]diprenorphine binding to intact cells increased 19.6-fold after etorphine treatment for 90 min, while naloxone IC50 values remained unaltered. This apparent increase in IC50 values was much lower, about 2-fold, when receptor binding was carried out in membranes isolated from cells treated with etorphine chronically. Furthermore, analysis of [3H]etorphine binding to such membranes in the presence of 10 mM Mg2+ indicated a loss of receptor binding sites with no change in apparent affinity, whereas [3H]diprenorphine binding revealed no significant alteration in either Bmax or Kd values. Therefore, during opiate receptor desensitization, a reduction of agonist high-affinity site occurs with no apparent alteration in total receptor number.