Vol. 60, Issue 3, 603-610, September 2001

Ca_v3.2 Channel Is a Molecular Substrate for Inhibition of T-Type Calcium Currents in Rat Sensory Neurons by Nitrous Oxide

Slobodan M. Todorovic, Vesna Jevtovic-Todorovic, Steven Mennerick, Edward Perez-Reyes, and Charles F. Zorumski

Departments of Anesthesiology (S.M.T., V.J.-T.) and Psychiatry (S.M.T., V.J.-T., S.M., C.F.Z.), Washington University School of Medicine, St. Louis, Missouri; and Department of Pharmacology, University of Virginia, Charlottesville, Virginia (E.P.-R.)

Although nitrous oxide (N₂O; laughing gas) remains widely used as an anesthetic and analgesic in clinical practice, its cellular mechanisms of action remain inadequately understood. In this report, we examined the effects of N₂O on voltage-gated Ca²⁺ channels in acutely dissociated small sensory neurons of adult rat. At subanesthetic concentrations, N₂O blocks low-voltage-activated, T-type Ca²⁺ currents (T currents), but not high-voltage-activated (HVA) currents. This blockade of T currents was concentration dependent, with an IC₅₀ value of 45 ± 13%, maximal block of 38 ± 12%, and Hill coefficient of 2.6 ± 1.0. No desensitization of the response or change in current kinetics was observed during N₂O application. The magnitude of T current blockade by N₂O does not seem to reflect any use- or voltage-dependent properties. In addition, T current blockade was not altered when intracellular GTP was replaced with guanosine 5'-(-thio)triphosphate or guanosine 5'-0-(2-thiodiphosphate) suggesting a lack of involvement of G-proteins in the inhibition. N₂O selectively blocked currents arising from the Ca_v3.2 but not Ca_v3.1 recombinant channels stably expressed in human embryonic kidney (HEK) cells in a concentration-dependent manner with an apparent affinity and potency similar to native dorsal root ganglion currents. Analogously, the block of Ca_v3.2 T currents exhibited little voltage- or use-dependence. These data indicate that N₂O selectively blocks T-type but not HVA Ca²⁺ currents in small sensory neurons and Ca_v3.2 currents in HEK cells at subanesthetic concentrations. Blockade of T currents may contribute to the anesthetic and/or analgesic effects of N₂O.