Effects of HI-6 on muscle acetylcholine receptor: analysis on minimal reaction model.

AIM: To study the action of 1-(2-hydroxyiminomethyl-1-pyridino)-3-(4-carbamoyl-1-pyridino)-2-oxapropane dichloride (HI-6) on skeletal muscle acetylcholine receptor (N2-ChR). METHODS: N2-ChR was expressed in Xenopus laevis oocyte after injection with mRNA extracted from denervated rat leg muscles. The inward membrane currents induced by various concentrations of carbamylcholine and effects of HI-6 or d-tubocurarine on the currents were measured with voltage clamp technique by fast cell flow of agents. The actions of HI-6 and d-tubocurarine on N2-ChR were analyzed by using the minimal reaction model. RESULTS: K of 40.05, 156.00, and 334.67 mumol.L-1 for HI-6, K of 0.02, 0.10, and 0.18 mumol.L-1 for d-tubocurarine were obtained by using the competing for single acetylcholine (ACh)-binding site model, the competing for two ACh-binding sites model, and the noncompetitive inhibition model, respectively. CONCLUSION: HI-6 and d-tubocurarine competed for two ACh-binding sites of N2-ChR with equal affinity to antagonize the effects of the agonist on N2-ChR. The N2-ChR inhibition by HI-6 is much weaker than that by d-tubocurarine.