Positive modulation of the alpha9alpha10 nicotinic cholinergic receptor by ascorbic acid

BOFFI JC; WEDEMEYER C; LIPOVSEK M; KATZ E; CALVO DJ; ELGOYHEN AB

BRITISH JOURNAL OF PHARMACOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2013 vol. 168 p. 954 - 965

0007-1188

Background and purpose: The activation of á9á10 nicotinic cholinergic receptors (nAChRs) present at the synapse between efferent olivocochlear fibers and cochlear hair cells can prevent acoustic trauma. Hence, pharmacological potentiators of these receptors could be useful therapeutically. In this work we characterize ascorbic acid as a positive modulator of recombinant á9á10 nAChRs. Experimental Approach: Acetylcholine (ACh)-evoked responses were analyzed under two-electrode voltage-clamp recordings in Xenopus laevis oocytes injected with á9 and á10 cRNAs. Key results: Ascorbic acid potentiated ACh responses in X. laevis oocytes expressing á9á10 (but not á4â2 or á7) nAChRs, in a concentration dependent manner, with an effective concentration range of 1-30 mM. The compound did not affect the receptor’s current-voltage profile nor its apparent affinity for ACh, but it significantly enhanced the maximal evoked currents (percentage of ACh maximal response, 240 ± 20%). This effect was specific for the L form of reduced ascorbic acid. Substitution of the extracellular cysteine residues present in loop C of the ACh binding site did not affect the potentiation. Ascorbic acid turned into a partial agonist of á9á10 nAChRs bearing a point mutation at the pore domain of the channel (TM2 V13´T mutant). A positive allosteric mechanism of action rather than an antioxidant effect of ascorbic acid is proposed. Conclusions and implications: The present work describes one of the few agents that activates or potentiates á9á10 nAChRs and leads to new avenues for designing drugs with potential therapeutic use in inner ear disorders.