Nishizaki T, Morales A, Gehle V M, Sumikawa K
Department of Psychobiology, University of California, Irvine 92717-4550.
Brain Res Mol Brain Res. 1994 Jan;21(1-2):99-106. doi: 10.1016/0169-328x(94)90382-4.
The nicotinic acetylcholine receptors (AChRs) from Torpedo electric organ and mouse muscles when expressed in Xenopus oocytes desensitize with different time courses. Initially, the role of cAMP-dependent phosphorylation on the gamma subunits in the different desensitization rates was investigated by expressing normal and mutant AChRs in the oocytes cultured in the presence of gentamicin. Mutant Torpedo AChRs lacking the potential cAMP-dependent phosphorylation sites in the gamma subunit appear to desensitize like normal Torpedo AChRs. Similarly, mutant mouse extrajunctional AChRs containing a newly created phosphorylation site in the gamma subunit appeared to desensitize like normal mouse AChRs, which lack the potential cAMP-dependent phosphorylation site in the gamma subunit. These results suggest that different rates of desensitization between the Torpedo and muscle extrajunctional AChRs are not attributable to differential cAMP-dependent phosphorylation of these AChRs. Subsequently, to determine whether gentamicin used in culturing oocytes differentially interacts with muscle junctional and extrajunctional AChRs, we analyzed rates of current decay following different gentamicin treatments. Both chronic and acute treatment with gentamicin profoundly accelerated the decay of whole-cell currents mediated by both types of AChR. The effect of prolonged gentamicin treatment on junctional AChRs was long lasting when compared to treatment on extrajunctional AChRs. Although the two types of AChR still desensitize differently in the absence of gentamicin, these results suggest that the characteristic desensitization of junctional and extrajunctional AChRs observed previously is largely due to differential interactions of gentamicin with the two types of AChR.
电鳐电器官和小鼠肌肉中的烟碱型乙酰胆碱受体（AChRs）在非洲爪蟾卵母细胞中表达时，脱敏过程的时间进程不同。最初，通过在庆大霉素存在下培养的卵母细胞中表达正常和突变型AChRs，研究了cAMP依赖性磷酸化对γ亚基在不同脱敏速率中的作用。γ亚基中缺乏潜在cAMP依赖性磷酸化位点的突变型电鳐AChRs似乎与正常电鳐AChRs一样发生脱敏。同样，γ亚基中含有新创建磷酸化位点的突变型小鼠接头外AChRs似乎与正常小鼠AChRs一样发生脱敏，正常小鼠AChRs的γ亚基中缺乏潜在的cAMP依赖性磷酸化位点。这些结果表明，电鳐和肌肉接头外AChRs之间不同的脱敏速率并非归因于这些AChRs的cAMP依赖性磷酸化差异。随后，为了确定培养卵母细胞时使用的庆大霉素是否与肌肉接头和接头外AChRs有不同的相互作用，我们分析了不同庆大霉素处理后的电流衰减速率。庆大霉素的慢性和急性处理均显著加速了两种类型AChR介导的全细胞电流的衰减。与对接头外AChRs的处理相比，长时间庆大霉素处理对接头AChRs的影响持续时间更长。尽管在没有庆大霉素的情况下，这两种类型的AChR仍以不同方式脱敏，但这些结果表明，先前观察到的接头和接头外AChRs的特征性脱敏很大程度上是由于庆大霉素与这两种类型AChR的不同相互作用所致。
