QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: mol.108.051060v1 75/1/166    most recent Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Liu, M. Articles by Dilger, J. P. Search for Related Content PubMed PubMed Citation Articles by Liu, M. Articles by Dilger, J. P.

Site Selectivity of Competitive Antagonists for the Mouse Adult Muscle Nicotinic Acetylcholine Receptor

Department of Anesthesiology, Stony Brook University, Stony Brook, New York

The muscle-type nicotinic acetylcholine receptor has two nonidentical binding sites for ligands. The selectivity of acetylcholine and the competitive antagonists (+)-tubocurarine and metocurine for adult mouse receptors is known. Here, we examine the site selectivity for four other competitive antagonists: cisatracurium, pancuronium, vecuronium, and rocuronium. We rapidly applied acetylcholine to outside-out patches from transfected BOSC23 cells and measured macroscopic currents. We have reported the IC₅₀ of the antagonists individually in prior publications. Here, we determined inhibition by pairs of competitive antagonists. At least one antagonist was present at a concentration producing 67% receptor inhibition. Metocurine shifted the apparent IC₅₀ of (+)-tubocurarine in quantitative agreement with complete competitive antagonism. The same was observed for pancuronium competing with vecuronium. However, pancuronium and vecuronium each shifted the apparent IC₅₀ of (+)-tubocurarine less than expected for complete competition but more than expected for independent binding. The situation was similar for cisatracurium and (+)-tubocurarine or metocurine. Cisatracurium did not shift the apparent IC₅₀ of pancuronium or vecuronium, indicating independent binding of these two pairs. The data were fit to a two-site, two-antagonist model to determine the antagonist binding constants for each site, L and L. We found L/L = 0.22 (range, 0.14-0.34), 20 (9-29), 21 (4-36), and 1.5 (0.3-2.9) for cisatracurium, pancuronium, vecuronium, and rocuronium, respectively. The wide range of L/L for some antagonists may reflect experimental uncertainties in the low affinity site, relatively poor selectivity (rocuronium), or possibly that the binding of an antagonist at one site affects the affinity of the second site.

Address correspondence to: James P. Dilger, Department of Anesthesiology, Stony Brook University, Stony Brook, NY 11790-8480. E-mail: james. dilger{at}stonybrook.edu