Fig. 4. The effects of isoflurane on inhibitory postsynaptic currents. (A ) Representative traces showing the effects of 310 μM (∼ 1 minimum alveolar concentration [MAC]) isoflurane on GABAergic synaptic currents. The principal effect is a prolongation in the current decay (in this example, the decay half-time is increased by approximately 100%), with little or no effect on peak height. Dots represent biexponential fits to the measured currents. (B ) The amplitude of the inhibitory postsynaptic current decreases monotonically with increasing concentrations of isoflurane. The points represent mean values (for an average of 12 cells). (C ) The increase in total charge transfer (the total area under the inhibitory postsynaptic current) is plotted as a percentage change from the control value. The points represent mean values (for an average of 12 cells). In each case, the line is drawn by eye and has no theoretic significance. The arrow marked “1 MAC” indicates a value for the isoflurane MAC for the rat of 310 μM. 14