Fig. 4. Effects of xenon and of halothane on voltage-gated K+currents (original tracings from two experiments). (A ) Transient (IK,to) and sustained (IK,sus) outward K+currents under control conditions (i.e. , absence of anesthetics). Currents were elicited by depolarizing steps to various potentials (see insert ). Test potentials from −60 to −20 mV yielded almost identical (i.e. , superimposed) traces. At the end of each 300-ms pulse, the sustained current (IK,sus) was determined. IK,towas considered to be the difference between the initial peak current and IK,sus. (B ) Effects of xenon on voltage-gated K+currents. The three traces were obtained during a depolarizing pulse to +60 mV, before, during, and after application of xenon. Note that the effect of xenon is confined to IK,to. (C ) Effects of halothane 0.75% on voltage-gated K+currents. Note that IK,toand IK,susare depressed.