Figure 1. Additive interactions between propofol and midazolam, or propofol and flurazepam, in hippocampal neurons. (A) Enhancement by 10 [micro sign]M propofol, 0.5 [micro sign]M midazolam, or the combination of midazolam and propofol of current activated by 3 [micro sign]M [small gamma, Greek]-aminobutyric acid (GABA) in hippocampal neurons. Responses shown are superimposed. The peak amplitude of current evoked by 3 [micro sign]M GABA, in the absence of presence of drug, was less than the current evoked by 600 [micro sign]M GABA. Responses were reversibly inhibited by bicuculline and reversed polarity at membrane potentials close to the chloride equilibrium potential (not shown). (B) The bar graphs indicate peak currents normalized to the amplitude of current evoked by 3 [micro sign]M GABA. (C,D) The interaction between midazolam and propofol, or flurazepam, and propofol was additive, because the measured response was not significantly different from the theoretical additive response (P < 0.05, Student's t test).