Receptor binding
A Popen curve for mouse muscle AChR expressed in Xenopus oocytes. In (a) is shown a cluster of AChR channel openings activated in response to 200 microM ACh. The cluster Popen=0.87. In (b) the relationship between cluster Popen and ACh concentration is shown. The data points show the mean plus or minus the standard error (n = 8 to 82 clusters) at each ACh concentration. The solid line shows the fit of the data to the reaction mechanism given in equation 7.24 where the agonist can both activate the receptor and block the open ion channel. The equilibrium constants for agonist binding to the two binding sites on the receptor were assumed to be equal KA and were estimated to be 22 microM, the ratio of channel opening to closing rate constants (beta/alpha) was 7.9, and the equilibrium constant for open channel block KB was 4.9 mM.