Persistent activation of α7 nicotinic ACh receptors associated with stable induction of different desensitized states

BACKGROUND AND PURPOSE GAT107 ((3aR, 4S, 9bS)-4-(4-bromo-phenyl)-3a, 4,5,9b-tetrahydro-3H-cyclopenta-[c] quinoline-8-sulfonamide) is a positive allosteric modulator (PAM) and agonist of alpha 7 nicotinic acetylcholine receptors (nAChRs) that can cause a prolonged period of primed potentiation of acetylcholine responses after drug washout. NS6740 is a silent agonist of alpha 7 nAChRs that has little or no efficacy for activating the ion channel but induces stable desensitization states, some of which can be converted into channel-active states by PAMs. Although GAT107 and NS6740 appear to stably induce different non-conducting states, both agents are effective treatment for inflammation and inflammatory pain models. We sought to better understand how both of these drugs that have opposite effects on channel activation could regulate signal transduction. EXPERIMENTAL APPROACH Voltage-clamp experiments were conducted with alpha 7 nAChRs expressed in Xenopus oocytes. KEY RESULTS Long-lived sensitivity to a PAM or to an agonist was produced by NS6740 or GAT107 respectively. With sequential applications, these two drugs induced varying levels of persistent activation, which is a unique condition for a receptor that is known for rapid desensitization. The non-conducting states induced by NS6740 or GAT107 differ in their sensitivity to an alpha 7 nAChR-selective antagonist and in how effectively they promote current. CONCLUSIONS & IMPLICATIONS Our data suggest that the persistent currents represent a dynamic interconversion between different stable desensitized states and the PAM-inducible conducting states. However, the similarity of NS6740 and GAT107 effects on inflammation and pain suggests that the different stable non-conducting states have common activity on signal transduction.