Nitrous oxide and xenon enhance phospholipid-N-methylation in rat brain synaptic plasma membranes

Halothane and isoflurane increase the rate of phospholipid methylation (PLM) in rat brain synaptosomal membranes, a process linked to the coupling of neuronal excitation to neurotransmitter release. In contrast, synaptic plasma membrane (SPM) Ca²⁺ ATPase (PMCA) pumping is reduced by exposure to halothane, isoflurane, xenon and nitrous oxide (N₂O). To examine further the relationship between PLM, PMCA and anesthetic action, we investigated the effect of clinically relevant concentrations of two less potent anesthetic gases, N₂O and xenon, on PLM in SPM. Biochemical assays were performed on SPM exposed to 1.3 MAC of N₂O (2 atm), 1.3 MAC of xenon (1.23 atm) or an equivalent pressure of helium for control. N₂O or xenon exposure increased PLM to 115% or 113%, respectively, of helium control (p < 0.02). Similar exposures to N₂O or xenon depressed PMCA activity to 78% and 85% of control (p < 0.05). Observations that PLM and PMCA are both altered by a wide variety of inhalation anesthetic agents at clinically relevant partial pressures lend support to a possible involvement and interaction of these processes in anesthetic action.