Figure 2. Concentration-response data for the loss-of-righting reflex in tadpoles (Rana temporaria) for R(+) etomidate ([circle, open]) and S(-) etomidate ([round bullet, filled]). Each data point represents the mean response for an average of 14 tadpoles. The lines are the best fits to a logistic function defined by Waud [17]for the analysis of quantal concentration-response curves (see Materials and Methods, Equation 1). For the R(+) isomer, the half-maximal effective concentration (EC50)= 3.4 +/- 0.1 micro Meter and the slope is n = 1.9 +/- 0.1, whereas for the S(-) isomer, EC50= 57 +/- 1 micro Meter and the slope is n = 2.9 +/- 0.2.