The local anaesthetics proadifen and adiphenine inhibit nicotinic receptors by different molecular mechanisms.

G SPITZMAUL,; GUMILAR F; J P DILGER,; BOUZAT C

BRITISH JOURNAL OF PHARMACOLOGY

British Parmacological Society

Año: 2009 vol. 157 p. 804 - 817

0007-1188

Background and purpose: Many local anaesthetics are noncompetitive inhibitors of nicotinic receptors (AChR). Proadifen induces a high-affinity state of the receptor, but its mechanism of action and that of an analog, adiphenine, is unknown. Experimental approach: We measured the effects of proadifen and adiphenine on single-channel and macroscopic currents of adult mouse muscle AChR (wild-type and mutant). We assessed the results in terms of mechanisms and sites of action. Key results: Both proadifen and adiphenine decrease the frequency of ACh-induced single-channel currents. Proadifen does not change cluster properties but adiphenine decreases cluster duration (36-fold at 100 µM). Preincubation with proadifen decreases the amplitude (IC50=19 µM) without changing the decay rate of macroscopic currents. In contrast, adiphenine does not change amplitude but increases the decay rate (IC50=15 µM). Kinetic measurements demonstrate that proadifen acts on the resting state to induce a desensitized state whose kinetics of recovery resemble those of ACh-induced desensitization. Adiphenine accelerates desensitization from the open state but previous application of the drug to resting receptors is required. Both drugs stabilize desensitized states, as evidenced by the decrease in the number of clusters elicited by high ACh concentrations. The inhibition by adiphenine is not affected by proadifen and the mutation aE262K decreases the sensitivity of the AChR only for adiphenine, indicating that these drugs act at different sites. Conclusions and implications: Two analogous local anaesthetics bind to different sites and inhibit AChR activity via different mechanisms and conformational states. These results provide new information on drug modulation of AChR.