Andreose J S, Fumagalli G, Sigworth F J, Caplan M J
Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT 06510, USA.
Proc Natl Acad Sci U S A. 1996 Jul 23;93(15):7661-6. doi: 10.1073/pnas.93.15.7661.
Newly synthesized membrane proteins travel from the Golgi complex to the cell surface in transport vesicles. We have exploited the ion channel properties of the nicotinic acetylcholine receptor (AChR) to observe in real time the constitutive delivery of newly synthesized AChR proteins to the plasma membrane in cultured muscle cells. Whole-cell voltage clamp was employed to monitor the current fluctuations induced by carbamylcholine upon the insertion into the plasma membrane of newly synthesized AChRs, following release from a 20 degrees C temperature block. We find that the transit of vesicles to the cell surface occurs within a few minutes after release of the block. The time course of electrical signals is consistent with many of the fusion events being instantaneous, although some appear to reveal the flickering of a fusion pore. AChR-containing vesicles can fuse individually or as conglomerates. Intracellular application of guanosine 5'-[gamma-thio]triphosphate inhibits the constitutive traffic of AChRs in most cells. Individual exocytotic vesicles carry between 10 and 300 AChR molecules, suggesting that AChRs may be packed extremely densely.
新合成的膜蛋白通过运输小泡从高尔基体复合体转运至细胞表面。我们利用烟碱型乙酰胆碱受体（AChR）的离子通道特性，实时观察新合成的AChR蛋白在培养的肌肉细胞中向质膜的组成型运输。在从20℃温度阻滞释放后，采用全细胞电压钳监测新合成的AChRs插入质膜时氨甲酰胆碱诱导的电流波动。我们发现，在阻滞释放后的几分钟内，小泡就会转运至细胞表面。电信号的时间进程与许多融合事件是瞬间发生的一致，尽管有些似乎显示出融合孔的闪烁。含AChR的小泡可以单独融合或聚集成团融合。在大多数细胞中，细胞内应用鸟苷5'-[γ-硫代]三磷酸可抑制AChRs的组成型运输。单个胞吐小泡携带10至300个AChR分子，这表明AChRs可能包装得极其密集。
