Preservation of "peripheral" benzodiazepine receptors: differential effects of freezing on [3H]Ro 5-4864 and [3H]PK 11195 binding.

The equilibrium binding constants of [3H]Ro 5-4864 (a "peripheral" benzodiazepine receptor ligand) to renal membranes preserved by various freezing techniques were investigated. The Bmax for [3H]Ro 5-4864 binding to membranes from kidneys preserved as unwashed homogenates stored at -80, -20, or 5 degrees C, whole kidneys stores at -20 or 5 degrees C or as washed homogenate stored at -20 degrees C was significantly decreased (approximately 35%). Only when kidneys were frozen intact (using a dry-ice/acetone slurry) and stored at -80 degrees C was the density of [3H]Ro 5-4864 binding unchanged. However, the Bmax of [3H]PK 11195 (a putative "peripheral" benzodiazepine receptor antagonist) binding to renal membranes was unchanged following storage techniques that reduced the density of [3H]Ro 5-4864 binding 38%. No change was observed in the Kd values for [3H]Ro 5-4864 and [3H]PK 11195 binding to renal membranes preserved under any condition tested. These results demonstrate a method for the preservation of [3H]Ro 5-4864 binding to renal membranes, and suggests that [3H]Ro 5-4864 and [3H]PK 11195 bind to unique sites on or near the "peripheral" benzodiazepine receptor. [corrected]