The Combined Application Of Volatile Anesthetics, Ketamine And Magnesium In Recombined NMDA Receptors

N - methyl - D - aspartate ( NMDA) receptors are important components of neurological processing. Ketamine and Magnesium block NMDA receptors and might therefore be useful analgesics, and combinations of magnesium and ketamine provide more effective analgesia. We investigated their interactions at NMDA receptors. Xenopus Oo-cytes, Expressed NR1/NR2A or NR1/NR2B glutamate receptors were studied. The effects of magnesium, racemic ketamine and its isomers, and the combination of magnesium and s ( + ) - ketamine on NMDA signaling were determined.Material and MethodsOocytes were obtained and defolliculated. The NMDA receptor consists of NR1 and NR2 subunits, which were obtained from Dr. P. J. Whiting ( UK). The experiments were performed at room temperature. Voltage clamp and related devices were used. Glutamate and glycine were used as NMDA receptor agonist; magnesium, s( + )-ketamine and isoflurane, sevoflurane, desflurane were apllied. The results were reported as Mean@ SEM, p < 0. 05 was considered sig-nificant.ResultsMagnesium and ketamine alone inhibited NMDA receptors non-competitively ( half - maximal inhibitory effect concentration: magnesium (4.2 ±1.2) ×10-4M at NR1/NR2A and (6.3±2.4) ×10-4M at NR1/NR2B; s( + ) - ketamine (4. 1 ± 2. 5) × 10-6 M at NR1/ NR2A and (3.0±0.3) ×10-6 M at NR1/NR2B. Half-maximal inhibitory concentration at NR1/NR2A receptors; 1. 30 ±0. 02MACs for isoflurane, 1. 18 ±0. 03MACs for desflurane, 1. 20 ±0. 06 MACs for sevoflurane; at NR1/NR2B receptor; 1. 33 ±0. 12MACs for isoflurane, 1.22 ±0. 08MAC for desflurane, and 1. 28 ± 0.08MACs for sevoflurane. On both NR1/NR2A and NR1/NR2B receptors, 50% inhibitory concentration for volatile anesthetics were reduced approximately 20% by magnesium, approximately 30% by s ( + ) - ketamine , and approximately 50% by the compounds in combination.DiscussionThe combined application of magnesium and ketamine decreased the half maximal inhibitory effect concentration more than 90% at both receptors. Isobolographic analysis demonstrated super - additive interactions. These findings may explain, in part, why combinations of ketamine and magnesium are more effective analgesics than either compound alone. During anesthesia patients are usually exposed con-comitantly to volatile anesthetics, we tested the hypothesis that volatile anesthetics interact with ketamine and/or magnesium at recombinantlyexpressed NMDA receptors. NR1/NR2A or NR1/NR2B receptors were expressed in Xenopus Oocytes. We determined the effects of isoflurane, sevoflurane and desflurane on NMDA receptor signalings, alone and in combination with s( + ) - ketamine(4.1uM on NR1/ NR2A,3. 0uM on NR1/NR2B) and magnesium(416uM on NR1/ NR2A, 629uM on NR1/NR2B) Volatile anesthetics inhibited NR1/ NR2A and NR1/NR2B glutamate receptor function in a reversible, concentration - dependent, voltage - insensitive and non - competitive manner.ConclusionVolatile anesthetic effects in NMDA receptors can be potentiated significantly by magnesium, s ( + ) - ketamine, or most profound -both. Therefore, the effects of ketamine and magnesium on NMDA receptors likely to be enhanced in the presence of volatile anesthetics.