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.