Figure 8. Effect of 50 micro Meter ketamine and 0.675 mM halothane on repetitively-stimulated potassium channels. (A) Repetitive depolarizations (10 0.1-s pulses to +20 mV from a V^hof -60 mV; interpulse interval as noted) results in a frequency-dependent cumulative reduction of current in the absence of drug. As expected, in Delta C318 channels, missing the C-terminal segment thought to influence C-type inactivation, [22]this type of inactivation was less pronounced than in Kv2.1 channels (although the data showing Delta C318 channels stimulated at 1-s and 5-s intervals are not included in the figure, a similar result to that shown with the 0.1-s protocol was obtained at these frequencies. (B) The progressive inhibition of potassium current seen under control conditions was significantly enhanced in both channels upon exposure to either anesthetic drug, although the enhancement was less pronounced in the deletion mutant than the parent channel. Interpulse interval = 0.1 s. Each data point indicates the mean of data obtained from 6 or 7 oocytes. The concentrations of 50 micro Meter ketamine and 0.675 mM halothane were chosen because they produce a similar level of inhibition (about 20%) of peak potassium current in Kv2.1.