We have previously shown that volatile anesthetics inhibit glutamate-stimulated [3H]MK-801 binding to the ionophore of NMDA receptor complexes in rat brain. In the present study, we examined the influence of enflurane and halothane on NMDA-stimulated45Ca uptake by a microvesicle fraction isolated from rat brain. NMDA stimulated45Ca uptake (30 sec) by rat brain microvesicles by up to 70% with an EC50 of 1.4±0.5 μM. The NMDA-stimulated45Ca uptake was inhibited by MK-801 and D-AP-5 with IC50's of ≈10 μM. Enflurane and halothane inhibited45Ca uptake stimulated by 100 μM NMDA by as much as 60-80% with IC50's of 0.2-0.3 mM, concentrations achieved during routine clinical use. Basal45Ca uptake measured in the absence of agonist was not affected by the anesthetics. Glycine did not affect the level of NMDA-stimulated45Ca uptake, but markedly reduced the inhibition of uptake caused by enflurane and halothane. Preincubation of microvesicles with NMDA resulted in a desensitization of NMDA-stimulated45Ca uptake, with a t1/2 of ≈20 sec. Enflurane and halothane diminished both the extent and rate of development of this desensitization, as did glycine. These findings support the idea that volatile anesthetic interference with neurotransmission at NMDA receptor complexes contributes to the development of the anesthetic state.
- NMDA receptors
- calcium flux
ASJC Scopus subject areas
- Cellular and Molecular Neuroscience