Ravdin P M, Nitkin R M, Berg D K
J Neurosci. 1981 Aug;1(8):849-61. doi: 10.1523/JNEUROSCI.01-08-00849.1981.
A protein neurotoxin (Bgt 3.1) present as a minor component in the venom of Bungarus multicinctus has been shown previously to block acetylcholine (ACh) sensitivity on chick ciliary ganglion (CG) neurons in cell culture. Alpha-bungarotoxin (Bgt. 2.2) binds to the neurons but does not block ACh sensitivity; the function of the Bgt. 2.2 binding site is unknown. The present studies demonstrate that Bgt 3.1 can induce the rapid internalization of Bgt 2.2 bound on the surface of CG and sympathetic neurons. The rapid internalization of bound Bgt 2.2 caused by Bgt. 3.1 can be seen with fluoresence microscopy using rhodamine-labeled Bgt 2.2 as the probe and by immunological techniques using anti-Bgt 2.2 antiserum to locate the bound 125I-Bgt 2.2. The rapid internalization is blocked by low temperature or by high concentrations of Bgt 2.2 and is not induced by Bgt 2.2 itself or by small cholinergic ligands. Bound 125I-Bgt 2.2 is released into the medium as degraded material after internalization is induced. Bgt 3.1 does not induce internalization of Bgt 2.2 bound to skeletal myotubes in culture nor does it induce the internalizaton of rhodamine-labeled nerve growth factor bound to sympathetic neurons, suggesting that its effect on neuronally bound Bgt 2.2 might be a specific one. Competition binding studies suggest that Bgt 3.1 may trigger the internalization of bound Bgt 2.2 by direct interaction with a Bgt 2.2 binding site. The effect of Bgt 3.1 on neuronal ACh sensitivity, however, does not depend on internalization of Bgt 2.2 binding sites since full inhibition of ACh sensitivity is still achieved by Bgt 3.1 under conditions where internalization is blocked. Neurons may have more than one class of Bgt 2.2 on the neurons. The internalization of Bgt 2.2 binding sites induced by Bgt 3.1 provides an unusual opportunity to study cellular mechanisms by which neurons can regulate the number and distribution of their surface components.
一种作为多环眼镜蛇毒液中次要成分的蛋白质神经毒素（Bgt 3.1），先前已被证明可在细胞培养中阻断鸡睫状神经节（CG）神经元上的乙酰胆碱（ACh）敏感性。α-银环蛇毒素（Bgt. 2.2）与神经元结合，但不阻断ACh敏感性；Bgt. 2.2结合位点的功能尚不清楚。目前的研究表明，Bgt 3.1可诱导结合在CG和交感神经元表面的Bgt 2.2快速内化。使用罗丹明标记的Bgt 2.2作为探针的荧光显微镜观察以及使用抗Bgt 2.2抗血清定位结合的125I-Bgt 2.2的免疫技术，均可观察到由Bgt. 3.1引起的结合型Bgt 2.2的快速内化。低温或高浓度的Bgt 2.2可阻断这种快速内化，而Bgt 2.2本身或小的胆碱能配体不会诱导这种内化。诱导内化后，结合的125I-Bgt 2.2以降解物质的形式释放到培养基中。Bgt 3.1不会诱导培养的骨骼肌管上结合的Bgt 2.2内化，也不会诱导结合在交感神经元上的罗丹明标记的神经生长因子内化，这表明其对神经元结合型Bgt 2.2的作用可能是特异性的。竞争结合研究表明，Bgt 3.1可能通过与Bgt 2.2结合位点直接相互作用来触发结合型Bgt 2.2的内化。然而，Bgt 3.1对神经元ACh敏感性的影响并不依赖于Bgt 2.2结合位点的内化，因为在阻断内化的条件下，Bgt 3.1仍能完全抑制ACh敏感性。神经元上可能存在不止一类Bgt 2.2。Bgt 3.1诱导的Bgt 2.2结合位点内化提供了一个独特的机会，来研究神经元调节其表面成分数量和分布的细胞机制。
