Received for publication December 19, 2005.
Revised February 16, 2006.
Accepted for publication February 27, 2006.

2-Fluoro-3-(4-nitro-phenyl)deschloroepibatidine is a novel potent competitive antagonist of human neuronal 42 nAChRs

Abstract

A patch-clamp technique in a whole-cell configuration was used to examine functional activity of recently developed 2-fluoro-3-(substituted phenyl) deschloroepibatidine analogs on two major subtypes of neuronal nAChRs, 42 and 34, that predominate in the central and peripheral nervous system, respectively. These epibatidine analogs have been shown previously to possess high binding affinity to 42 but not to 7 nAChRs and to inhibit nicotine-induced analgesia in behavioral pain tests. The 2-fluoro-3-(4-nitro-phenyl)deschloroepibatidine (4-nitro-PFEB) analog exhibited the most pronounced antagonist activity among these analogs when tested electrophysiologically on 42 nAChRs. It inhibited ACh-induced currents in a concentration-dependent manner with an IC₅₀ of 0.1 µM and inducing complete inhibition at ~1 µM concentration. 4-Nitro-PFEB at 0.1 µM concentration produced a four-fold rightward shift in the ACh concentration-response curve without altering maximum ACh-induced response. The inhibitory effect of 4-nitro-PFEB was voltage- and use-independent, and partially reversible at its 1 µM concentration. The rise and decay kinetics of ACh-induced currents was not altered in the presence of 4-nitro-PFEB. In contrast to 42 nAChRs, this compound did not affect 34 nAChR-mediated currents at 1µM (IC₅₀~63.9 µM). Overall, these functional data agree with previous binding and behavioral findings and suggest collectively that 4-nitro-PFEB is the most effective and selective antagonist of 42 versus 34 and 7 nAChRs among the tested analogs, acting on 42 nAChR through a competitive mechanism with a potency 17-fold higher than that of dihydro--erythroidine.

Key words: Nicotinic cholinergic, Ion channel regulation, Func. analysis receptor/ion channel mutants, Drug tolerance/dependence