Key roles of hydrophobic rings of TM2 in gating of the a9a10 nicotinic cholinergic receptor

PLAZAS PV; DE ROSA MJ; GOMEZ-CASATI ME; VERBITSKY M; WEISSTAUB N; KATZ E; BOUZAT C; ELGOYHEN AB

BRITISH JOURNAL OF PHARMACOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Año: 2005 p. 963 - 974

0007-1188

We have performed a systematic mutagenesis of three hydrophobic rings (170, 130 and 90) within transmembrane region (TM) 2 of the a9a10 nicotinic cholinergic receptor (nAChR) to a hydrophilic (threonine) residue and compared the properties of mutant receptors reconstituted in Xenopus laevis oocytes. 2 Phenotypic changes in a9a10 mutant receptors were evidenced by a decrease in the desensitization rate, an increase in both the EC50 for ACh as well as the efficacy of partial agonists and the reduction of the allosteric modulation by extracellular Ca2þ. 3 Mutated receptors exhibited spontaneous openings and, at the single-channel level, an increased apparent mean open time with no major changes in channel conductance, thus suggesting an increase in gating of the channel as the underlying mechanism. 4 Overall, the degrees of the phenotypes of mutant receptors were more overt in the case of the centrally located V130T mutant. 5 Based on the atomic model of the pore of the electric organ of the Torpedo ray, we can propose that the interactions of side chains at positions 130 and 90 are key ones in creating an energetic barrier to ion permeation. 6 In spite of the fact that the roles of the TM2 residues are mostly conserved in the distant a9a10 member of the nAChR family, their mechanistic contributions to channel gating show significant differences when compared to other nAChRs. These differences might be originated from slight differential intramolecular rearrangements during gating for the different receptors and might lead each nAChR to be in tune with their physiological roles.