Regulation of alpha4beta2 nicotinic receptor desensitization by calcium and protein kinase C.
Regulation of alpha4beta2 nicotinic receptor desensitization by calcium and protein kinase C.
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发表时间：
1999
影响因子：
3.6
通讯作者：
C. Fenster;M. Beckman;J. Parker;E. B. Sheffield;T. Whitworth;M. Quick;R. Lester
中科院分区：
文献类型：
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作者：
C. Fenster;M. Beckman;J. Parker;E. B. Sheffield;T. Whitworth;M. Quick;R. Lester
神经元烟碱型乙酰胆碱受体(NAChR)脱敏被认为是长期尼古丁受体数量和功能变化的触发因素，在长期服用尼古丁后观察到的水平与吸烟者相似。调节脱敏的因素可能会潜在地影响长期接触尼古丁的结果。研究了钙离子和蛋白激酶C(PKC)在非洲爪哇卵母细胞表达的α4β2 nAChRs脱敏中的作用。尼古丁(300 nM；30min)对有钙离子存在的α4β2受体的脱敏作用呈双相发展，快和慢的指数时间常数分别为Tauf=1.4min(相对幅度的65%)和taus=17min。脱敏后的恢复可以用一个单一指数来描述，taurec=43min。用Ba2+替代外钙后，恢复基本消失，并被PKC抑制剂calphostin C(taurec=48min)减缓。反之，PKC激活剂佛波醇-12-肉豆蔻酸酯-13-醋酸酯(taurec=14min)或磷酸酶抑制剂环孢菌素A(taurec=8min)可提高回收率。含有突变的α4亚单位的α4β2受体缺乏共同的PKC磷酸化位点，在脱敏后几乎没有恢复。基于双态脱敏循环模型，提出了长期尼古丁处理后，α4β2 nAChRs在“深度”脱敏状态下积聚，从这种状态恢复非常缓慢。我们认为，依赖于PKC的α4亚基的磷酸化改变了从“深”到“浅”脱敏构象的转换速率，并有效地提高了脱敏的总恢复率。长期的去磷酸化可能是慢性尼古丁治疗后观察到的α4β2受体“永久”失活的基础。
Neuronal nicotinic acetylcholine receptor (nAChR) desensitization is hypothesized to be a trigger for long-term changes in receptor number and function observed after chronic administration of nicotine at levels similar to those found in persons who use tobacco. Factors that regulate desensitization could potentially influence the outcome of long-lasting exposure to nicotine. The roles of Ca2+ and protein kinase C (PKC) on desensitization of alpha4beta2 nAChRs expressed in Xenopus laevis oocytes were investigated. Nicotine-induced (300 nM; 30 min) desensitization of alpha4beta2 receptors in the presence of Ca2+ developed in a biphasic manner with fast and slow exponential time constants of tauf = 1.4 min (65% relative amplitude) and taus = 17 min, respectively. Recovery from desensitization was reasonably well described by a single exponential with taurec = 43 min. Recovery was largely eliminated after replacement of external Ca2+ with Ba2+ and slowed by calphostin C (taurec = 48 min), an inhibitor of PKC. Conversely, the rate of recovery was enhanced by phorbol-12-myristate-13-acetate (taurec = 14 min), a PKC activator, or by cyclosporin A (with taurec = 8 min), a phosphatase inhibitor. alpha4beta2 receptors containing a mutant alpha4 subunit that lacks a consensus PKC phosphorylation site exhibited little recovery from desensitization. Based on a two-desensitized-state cyclical model, it is proposed that after prolonged nicotine treatment, alpha4beta2 nAChRs accumulate in a "deep" desensitized state, from which recovery is very slow. We suggest that PKC-dependent phosphorylation of alpha4 subunits changes the rates governing the transitions from "deep" to "shallow" desensitized conformations and effectively increases the overall rate of recovery from desensitization. Long-lasting dephosphorylation may underlie the "permanent" inactivation of alpha4beta2 receptors observed after chronic nicotine treatment.