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

PURPOSE: The cellular target site(s) for anesthetic action remain controversial. In this study we have examined any interaction of i.v. anesthetics (thiopental, pentobarbital, ketamine, etomidate, propofol, alphaxalone), local anesthetics (lidocaine, prilocaine, procaine and tetracaine), and the non anesthetic barbiturate, barbituric acid with the omega-conotoxin MVII(A) binding site on N-type voltage sensitive Ca2+ channels in rat cerebrocortical membranes.

METHODS

[125I] omega-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 degrees C using fresh cerebrocortical membranes (5 microg of protein). Non-specific binding was defined in the presence of excess (10(-8) M) omega-conotoxin MVII(A). The interaction of i.v. (alphaxolone, etomidate, propofol, pentobarbitone, ketamine and thiopentone), local (lidocaine, prilocaine, procaine and tetracaine) anesthetics and barbituric acid was determined by displacement of [125I] omega-conotoxin MVII(A) (approximately 1 pM).

RESULTS

The binding of [125I] omega-conotoxin was concentration-dependent and saturable with Bmax and Kd of 223 +/- 15 fmol/mg protein and 2.13 +/- 0.14 pM, respectively. Unlabelled omega-conotoxin MVII(A) displaced [125I] omega-conotoxin MVII(A) yielding a pKd of 11.04 +/- 0.04 (9.2 pM). All i.v. and local anesthetics at clinically relevant concentrations did not show any interaction with the omega-conotoxin MVII(A) binding site.

CONCLUSION

The present study suggests that omega-conotoxin MVII(A) binding site on N-type voltage sensitive Ca2+ channels may not be a target for i.v. and local anesthetic agents.