Figure 4. Analysis of flicker K+channel blockade by ketamine. (A) Recordings of a single channel from an outside-out patch in 105 mM Ko(control) and after addition of 200 micro Meter S(+) and R(-) ketamine to the external solution. Opening events are shown as downward deflections; c and arrowhead indicate the current level of the closed state. Eh=-90 mV; pipette contains KCl1; filter frequency, 2 kHz; sample interval, 250 micro second; temperature, 15 +/- 1 degrees Celsius. (B) Estimation of single-channel amplitude using amplitude histograms from the same experiment as in Figure 4(A). Curves represent the sum of two Gaussian curves for the closed and open state of the channel. Filter frequency, 10 kHz; sample interval, 26 micro second; bin width, 0.2 pA. Histograms are normalized as n/nmax, where n is the number of points in each bin and nmaxis the total number of points. The single-channel current is measured as the difference between the two Gaussian peaks. (C) Kinetic properties of single flicker K+channel block. Frequency density is plotted versus time. Histograms were fitted with one exponential Tcf= 0.17 ms in control solution and two exponentials in ketamine, revealing mean closed times taucf= 0.15 ms and taucs= 2.47 ms in S(+) and taucf= 0.14 ms and taucs= 3.44 ms in R(-) ketamine. Filter frequency was 5 kHz and sample interval was 20 micro second.