Effects of intravenous and local anesthetic agents on ω-conotoxin MVII(A) binding to rat cerebrocortex

Abstract

Purpose: The cellular target site(s) for anesthetic action remain controversial. In this study we have examined any interaction of iv anesthetics (thiopental, pentobarbital, ketamine, etomidate, propofol, alphaxalone), local anesthetics (lidocaine, prilocaine, procaine and tetracaine), and the non anesthetic barbiturate, barbituric acid with the ω-conotoxin MVII(A) binding site on N-type voltage sensitive Ca2+ channels in rat cerebrocortical membranes. Methods: [125I] ω-conotoxin MVII(A) binding assays were performed in 0.5 ml volumes of Tris. HCl buffer containing BSA 0.1% for 30 min at 20°C using fresh cerebrocortical membranes (5 μg of protein). Non-specific binding was defined in the presence of excess (10-8 M) ω-conotoxin MVII(A). The interaction of iv (alphaxolone, etomidate, propofol, pentobarbitone, ketamine and thiopentone), local (lidocaine, prilocaine, procaine and tetracaine) anesthetics and barbituric acid was determined by displacement of [125I] ω-conotoxin MVII(A) (I pM). Results: The binding of [125I] ω-conotoxin was concentration-dependent and saturable with B(max) and K(d) of 223 ± 15 fmol/mg protein and 2.13 ± 0.14 pM, respectively. Unlabelled ω-conotoxin MVII(A) displaced [125I] ω-conotoxin MVII(A) yielding a pK(d) of 11.04 ± 0.04 (9.2 pM). All iv and local anesthetics at clinically relevant concentrations did not show any interaction with the ω-conotoxin MVII(A) binding site. Conclusion: The present study suggests that ω-conotoxin MVII(A) binding site on N-type voltage sensitive Ca2+ channels may not be a target for iv and local anesthetic agents.