Benzodiazepine receptors in rat brain: action of Triton X-100 and localization in relation to the synaptic region.

Membranes were isolated from the cerebral cortices of rat brain and submitted to binding with 3H-flunitrazepam (3H-FNZP). Specific binding gave a hyperbolic saturation curve reaching a maximum between 10 - 12 nM suggesting a single population of sites. By Scatchard analysis a KD = 4 nM and a Bmax = 407 fmol/mg protein was obtained; the Hill number was 0.97. The effect of Triton X-100 was analyzed between concentrations of 6.4 x 10(-8) and 5 x 10(-1)%. With 6.4 x 10(-6) and 6.4 x 10(-3)% there is an activation of the binding without loss of protein. This activation is not reversed by washing. At 6.4 x 10(-2)% or higher concentrations there is an inhibition that is partially reversed and also solubilization of some receptors. The activation with low detergent is due to an increase in Bmax without change in KD. With 2 x 10(-1)% and 5 x 10(-1)% Triton X-100 there is considerable decrease in Bmax and in th latter case, an increase in affinity, as well. The results obtained through the action of Triton X-100 suggest that a proportion of benzodiazepine receptors are localized presynaptically. There findings are discussed in relation to previous studies from this laboratory on the localization of other central receptors with reference to the synaptic region.