Temperature Dependence of [3H]Ro 15–1788 Binding to Benzodiazepine Receptors in Human Postmortem Brain Homogenates

The temperature dependence of in vitro binding of [3H]Ro 15-1788 to benzodiazepine receptors in human postmortem neocortex and neocerebellum homogenates was studied. An increase of the equilibrium dissociation constants (KD) from 1.40 nmol/L and 1.04 nmol/L at 4 degrees C to 6.10 nmol/L and 8.91 nmol/L at 37 degrees C was found for neocortex and neocerebellum, respectively. In contrast, maximal binding (Bmax) remained in the range of 30-35 fmol/mg for neocortex and 24-27 fmol/mg of tissue (wet weight) for neocerebellum at all the temperatures. The KD of 6.10 nmol/L for neocortex at 37 degrees C in vitro is of the same order as the KD of 10 nmol/L obtained by positron emission tomography for [11C]Ro 15-1788 binding to benzodiazepine receptors in the human neocortex in vivo. The differences in KD between in vitro and in vivo benzodiazepine receptor binding to human neocortex and cerebellum seem to be due at least partially to temperature differences of in vitro and in vivo studies.