Association (A) and dissociation (B) kinetics of 2 nM ³H-etomidate with adrenal membranes. (A) ³H-etomidate was incubated with membranes for the indicated times before filtering. Each data point is the mean ± SD (n = 3) radioactivity measured in the washed filter. The curve is a fit of the data set to a single exponential equation to define the ³H-etomidate association half-time (1.1 min). (B) ³H-etomidate was equilibrated with membranes for 30 min. Excess cold etomidate (100 µM) was then added, and the mixture was filtered at the indicated incubation time after adding the cold etomidate. Each data point is the mean ± SD (n = 3) radioactivity measured in the washed filter. The curve is a fit of the data to a single exponential equation to define the ³H-etomidate dissociation half-time (1.1 min). The final protein concentration was 0.07 mg/ml. Units of radioactivity are in counts per minute (CPM).