Thymopoietin, a thymic polypeptide, potently interacts at muscle and neuronal nicotinic α-bungarotoxin receptors

Publisher Website
Google Scholar
Abstract
Current studies suggest that several distinct populations of nicotinic acetylcholine (ACh) receptors exist. One of these is the muscle-type nicotinic receptors with which neuromuscular nicotinic receptor ligands and the snake toxin α-bungarotoxin interact. α-Bungarotoxin potently binds to these nicotinic receptors and blocks their function, two characteristics that have made the α-toxin a very useful probe for the characterization of these sites. In neuronal tissues, several populations of nicotinic receptors have been identified which, although they share a nicotinic pharmacology, have unique characteristics. The α-bungarotoxin-insensitive neuronal nicotinic receptors, which may be involved in mediating neuronal excitability, bind nicotinic agonists with high affinity but do not interact with α-bungarotoxin. Subtypes of these α-toxin-insensitive receptors appear to exist, as evidenced by findings that some are inhibited by neuronal bungarotoxin whereas others are not. In addition to the α-bungarotoxin-insensitive sites, α-bungarotoxin-sensitive neuronal nicotinic receptors are also present in neuronal tissues. These latter receptors bind α-bungarotoxin with high affinity and nicotinic agonists with an affinity in the μM range. The function of the nicotinic α-bungarotoxin receptors are as yet uncertain. Thymopoietin, a polypeptide linked to immune function, appears to interact specifically with nicotinic receptor populations that bind α-bungarotoxin. Thus, in muscle tissue where α-bungarotoxin both binds to the receptor and blocks activity, thymopoietin also potently binds to the receptor and inhibits nicotinic receptormediated function. In neuronal tissues, thymopoietin interacts only with the nicotinic α-bungarotoxin site and not the α-bungarotoxin-insensitive neuronal nicotinic receptor population. These observations that thymopoietin potently and specifically interacts with nicotinic α-bungarotoxin-sensitive receptors in neuronal and muscle tissue, together with findings that thymopoietin is an endogenously occurring agent, could suggest that this immune-related polypeptide represents a ligand for the α-bungarotoxin receptors. The function of thymopoietin at the α-bungarotoxin receptor is as yet uncertain; however, a potential trophic, as well as other roles are suggested.