ISOFLURANE INCREASES THE UPTAKE OF GLUTAMATE IN SYNAPTOSOMES FROM RATCEREBRAL-CORTEX

We have studied the effect of increasing concentrations of isoflurane on high- and low-affinity uptake of L-glutamate using synaptosomes fro m rat cerebral cortex. In the high-affinity uptake range, 0.5% isoflur ane had no effect on uptake velocity, while 1.5% and 3.0% isoflurane c aused an increase in mean Vmax to 131 (SEM 54) and 210 (103)% of contr ol, respectively. There was no significant change in the K-m value. Vm ax and K-m values for low-affinity uptake of L-glutamate were unchange d by 1.5% isoflurane. These results provide evidence for an isoflurane -induced increase in high-affinity uptake of glutamate into presynapti c terminals. This effect may contribute to a reduction of transmitter in the synaptic cleft and thereby decreased excitatory synaptic transm ission.