Studies on the properties of benzodiazepine-binding sites from calf cortex

[3H]Flunitrazepam ([3H]FNZ) specifically binds to a single class of sites in calf cortex homogenate at a level of about 1 pmol/mg protein. Essentially all binding sites sediment after a 30 min centrifugation at 20,000 X g. The affinity of the sites decreases with increasing temperature both in a homogenate and in a washed membranes preparation. Binding sites in the washed membranes preparation display lower affinity than those in the homogenate (e.g., KD of 14.8 nM vs. 7.6 nM respectively at 37 degrees C), but membrane-sites affinity can be increased by aliquots of high-speed supernatant as well as by GABA (> 10(-7) M). GABA has only a small effect on the on-reaction but slows the off-reaction. The binding sites require chloride ions (approximately 100 mM) for optimal activity, are inhibited by Hg+2, and are partially released into a high-speed supernatant by several detergents.