Abstract: Aim The kinetics of nicotinic acetylcholine receptor (N-AChR) was stadied. Methods The saturation experiments of Torpedo electric organ N-AChR were taken with ¹²⁵I-a-BuTX. The results were calculated by Scatfit program. Experiments were then performed to study the kinetics of dissociation of a-BuTX and nicotine from N-AChR, respectively. When their binding reached saturation, an excess of 1000 times a-BuTX or nicotine was added. The saturation binding properties of the N-AChR extracted from leg muscles of the 13th day chick embroys and optic lobes of the 20th day chick embroys were studied. The results were calculated by Scatfit program. The othe experiments were taken to observe the competition between mcotine and ¹²⁵I-a BuTX for binding with Torpedo, optic lobe and skeletal muscle of the chick N-AChRs.Results The saturation experiments of Torpedo electric organ N-AChR resulted in a Scatchard plot of hyperbola which responded to the model of two kinds of receptor with on eligand. The difference of and B max between high affinity binding site and low affinity bineing site was significant. The dissaciation experiment showed that the fast dissociation rate of tow ligands was 500 times more than that of the slow dissociation rate. This result suggested that there may be two subtype N-AChRs. The saturation binding properties of N-AChR of leg muscles and optic lobe of the chick embroys revealed a Scatchard plot of two kinds of N-AChR indicating a single type of site. The binding affinity of receptor of optic lobe was 100 times more than that of muscles. In competition for Torpedo receptor by nicotine and ¹²⁵I-a BuTX, the values of ICoo were different:which suggested that two kinds of receptor sites were existent. In competition of Nicotine and ¹²⁵I-a-BuTX for optic lobe and skeletal muscles of the chick N-AChR, the value ICso of skeletal muscles N-AChR was 7.7 times higher than that of optic lobe.It indicated that two kinds of N-AChR subtype existed in the optic lobe and in the skeletal muscles of chick respectively.Conclusion N-AChR of Torpedo electric organ contains two kinds of subtype receptors.N-AChR of optic lobe of chick embroys is one subtype receptor,and N-AChR of skeletal muscles of chick embroy is another subtype receptor.

Key words: N-AChR, a-BuTX, saturalion experiment, competion experiment