Chiang P K, Butler D L, Brown N D
Applied Biochemistry Branch, Walter Reed Army Institute of Research, Washington, DC 20307-5100.
Life Sci. 1991;49(6):PL13-9. doi: 10.1016/0024-3205(91)90591-x.
(+)-Anatoxin-a (ANTX) stimulated guinea pig ileum contraction with a potency similar to that of acetylcholine (ACh); the stimulation was blocked by tubocurarine, hexamethonium, or atropine. Although the contraction stimulated by ANTX was blocked by atropine, no specific inhibition of the binding of [3H]N-methylscopolamine to ileum membranes was observed in the presence of ANTX. Furthermore, ANTX failed to stimulate the secretion of alpha-amylase from pancreatic acinar cells, a process that is activated by cholinergic agonists at the muscarinic receptors. When the ileum itself was stimulated by ACh, the contraction was not blocked by either hexamethonium or tubocurarine. Preincubation of the ileum with hemicholinium caused a 50% reduction in the ability of ANTX to stimulate contraction. Based upon these data, it was inferred that ANTX binds to postganglionic synaptic nicotinic receptors in the ileum, thus releasing endogenous ACh, which in turn causes ileum contraction by interacting with the postsynaptic muscarinic receptors. It was also observed that thymopentin (TP-5), a pentapeptide corresponding to positions 32-36 of thymopoietin, blocked the stimulation of ileum contraction by ANTX.
（+）-anatoxin-a（ANTX）刺激豚鼠回肠收缩，其效力与乙酰胆碱（ACh）相似；该刺激可被筒箭毒碱、六甲铵或阿托品阻断。尽管ANTX刺激的收缩可被阿托品阻断，但在存在ANTX的情况下，未观察到[3H]N-甲基东莨菪碱与回肠膜结合的特异性抑制。此外，ANTX未能刺激胰腺腺泡细胞分泌α-淀粉酶，而该过程是由毒蕈碱受体处的胆碱能激动剂激活的。当回肠自身受到ACh刺激时，其收缩不受六甲铵或筒箭毒碱的阻断。用半胱氨酸预孵育回肠会使ANTX刺激收缩的能力降低50%。基于这些数据，推断ANTX与回肠中的节后突触烟碱受体结合，从而释放内源性ACh，进而通过与突触后毒蕈碱受体相互作用引起回肠收缩。还观察到胸腺五肽（TP-5），一种与胸腺生成素第32-36位相对应的五肽，可阻断ANTX对回肠收缩的刺激。
