Figure 4. Modulation of macroscopic Potassium sup + channel current by low (0.4 mM equivalent to 0.7%) and high (0.9 mM, equivalent to 1.5%) concentrations of halothane in canine cerebral arterial muscle cells dialized with zero Calcium2+ and 10 mM EGTA. (Top) The pulse protocol and actual recordings of macroscopic Potassium sup + current traces in control solution and after exposure to low or high doses of halothane. Voltage steps from a holding potential (HP) of 60 mV to the corresponding potentials elicited an outward current whose amplitude was depressed markedly and reversibly by halothane. (Bottom) The peak current-voltage relationship in control solution and after exposure to low and high doses of halothane, 0.4 (n = 6) and 0.9 mM (n = 6), respectively. Cells were depolarized progressively from a HP of 60 mV to the corresponding potentials indicated on the abscissa. Points with error bars represent the mean plus/minus SEM.