Activation and desensitization of the α7 nAChRs. Activation and desensitization of the α7 nAChRs. (A) Activation of α7 nAChRs by brief pulses of nicotine at increasing concentrations compared with a saturating ACh test pulse. Plot of the peak inward current, as a function of the logarithm of the nicotine concentration, yields a typical concentration-response curve as shown by ○ (C). Data were normalized versus the current evoked by 1.28 mM ACh. (B) Sustained exposure to nicotine inhibits the current evoked by a brief ACh test pulse (100 μM). Plot of the peak ACh-evoked current as a function of the logarithm of nicotine concentration yields the inhibition curve shown by the ● (C). Inhibition was scaled to 50% of the maximal response corresponding to the fraction of current evoked by 100 μM ACh. Continuous curves through the data points are the best fits obtained with a Hill equation (D. Bertrand, personal communication). Daniel Bertrand et al. Pharmacol Rev 2015;67:1025-1073 Copyright © 2015 by The American Society for Pharmacology and Experimental Therapeutics