Effects of intravenous and local anesthetic agents on omega-conotoxin MVIIA binding to rat cerebrocortex

Purpose: The cellular target site(s) for anesthetic action remain controver sial. In this study we have examined any interaction of iv anesthetics (thi opental, pentobarbital, ketamine; etomidate, propofol, alphaxalone), local anesthetics (lidocaine, prilocaine, procaine and tetracaine), and the non a nesthetic barbiturate, barbituric acid with the omega-conotoxin MVIIA bindi ng site on N-type voltage sensitive Ca2+ channels in rat cerebrocortical me mbranes. Methods: [I-125] omega-conotoxin MVIIA binding assays were performed in 0.5 ml volumes of Tris.HCl buffer containing BSA 0.1% for 30 min at 20 degrees C using fresh cerebrocortical membranes (5 mu g of protein). Non-specific binding was defined in the presence of excess (10(-8) M) omega-conotoxin MV IIA. The interaction of iv (alphaxolone, etomidate, propofol, pentobarbiton e, ketamine and thiopentone), local (lidocaine; prilocaine, procaine and te tracaine) anesthetics and barbituric acid was determined by displacement of [I-125] omega-conotoxin MVIIA (similar to 1 pM), Results: The binding of [I-125] omega-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 omega-conotoxin MYIIA displaced [I-125] omega-conotoxin MVIIA yielding a pK(d) of 11.04 +/- 0.04 (9.2 pM). All iv and local anesthetics at clinically relevant concentrations did not show an y interaction with the omega-conotoxin MVIIA binding site. Conclusion: The present study suggests that omega-conotoxin MVIIA binding s ite on N-type voltage sensitive Ca2+ channels may not be a target for iv an d local anesthetic agents.