RESUMO
Aim The kinetics of nicotinic acetylcholine receptor (N-AChR) was stadied. MethodsThe saturation experiments of Torpedo electric organ N-AChR were taken with125I-?-BuTX. The results were calculated by Scatfit program. Experiments were thenperformed to study the kinetics of dissociation of ?-BuTX and nicotine from N-AChR,respectively. When their binding reached saturation, an excess of 1000 times ?-BuTX ornicotine was added. The saturation binding properties of the N-AChR extracted fromleg muscles of the 13th day chick embroys and optic lobes of the 20th day chick em-broys were studied. The results were calculated by Scatfit program. The othe experi-ments were taken to observe the competition between mcotine and 125I-?-BuTX forbinding with Torpedo, optic lobe and skeletal muscle of the chick N-AChRs. ResultsThe saturation experiments of Torpedo electric organ N-AChR resulted in a Scatchardplot of hyperbola which responded to the model of two kinds of receptor with on eli-gand.The difference of and B max between high affinity binding site and low affnitybineing site was significant. The dissaciation experiment showed that the fast dissocia-tion rate of tow ligands was 500 times more than that of the slow dissociation rate. Thisresult suggested that there may be two subtype N-AChRs.The saturation bindingproperties of N-AChR of leg muscles and optic lobe of the chick embroys revealed aScatchard plot of two kinds of N-AChR indicating a single type of site. The bindingaffinity of receptor of optic lobe was 100 times more than that of muscles. In competi-tion for Torpedo receptor by nicotine and 125I-?-BuTX, the values of IC50 were different:which suggested that two kinds of receptor sites were existent. In competition ofNicotine and 125I-?-BuTX for optic lobe and skeletal muscles of the chick N-AChR, thevalue IC50 of skeletal muscles N-AChR was 7. 7 times higher than that of optic lobe. Itindicated that two kinds of N-AChR subtype existed in the optic lobe and in theskeletal muscles of chick respectively. Conclusion N-AChR of Torpedo electric organcontains two kinds of subtype receptors. N-AChR of optic lobe of chick embroys is onesubtype receptor, and N-AChR of skeletal muscles of chick embroy is another subtypereceptor.