NEURONAL NICOTINIC THREONINE-FOR-LEUCINE-247 ALPHA(7) MUTANT RECEPTORS SHOW DIFFERENT GATING KINETICS WHEN ACTIVATED BY ACETYLCHOLINE OR BYTHE NONCOMPETITIVE AGONIST 5-HYDROXYTRYPTAMINE

Mutation of the highly conserved leucine residue (Leu-247) converts 5- hydroxytryptamine (5HT) from an antagonist into an agonist of neuronal homomeric alpha(7) nicotinic acetylcholine receptor expressed in Xeno pus oocytes. We show here that acetylcholine (AcCho) activates two cla sses of single channels with conductances of 44 pS and 58 pS, similar to those activated by 5HT, However, the mean open lime of AcCho-gated ion channels (11 ms) is briefer than that of 5HT-gated ion channels (1 8 ms), Furthermore, whereas the open time of AcCho channels lengthens with hyperpolarization, that of SIFT channels is decreased. In voltage -clamped oocytes, the apparent affinity of the alpha(7) mutant recepto r for 5HT is not modified by the presence of dihydro-beta-erythroidine , which acts on the AcCho binding site in a competitive manner. This i ndicates a noncompetitive action of 5HT an nicotinic acetylcholine rec eptors, Considered together, our findings show that AcCho gates alpha( 7) mutant channels with similar conductance but with different kinetic profile than the channels gated by 5HT, suggesting that the two agoni sts act on different docking sites. These results will help to underst and the crosstalk between cholinergic and serotonergic systems in the central nervous system.