Biochemical properties of spiperone binding to rat brain membranes

The biochemical properties of H-spiperone binding in vitro were studied systematically using a crude membrane homogenate of rat corpus striatum and separation by filtration. Scatchard analysis revealed a single high affinity site with a KD of 0.14 nM and Bmax of 26 fmol/mg of tissue. The dissociation constant obtained by measurements at equilibrium was similar to that obtained by measuring the rates of association and dissociation. The high affinity binding was stereospecific, thermolabile and highly pH dependent, being maximal from pH 7.6 to 7.8. Varying the concentration of Na+, Ca++, Mg++, Mn++, and Tris buffer had no significant effect on the amount of specific spiperone binding. Of the neurotransmitters, dopamine was the most potent inhibitor of specific spiperone binding, followed by serotonin, epinephrine, and norepinephrine. Apomorphine was more potent than dopamine, but less so than chlorpromazine and unlabelled spiperone. In eight regions of the rat brain, a direct correlation between the number of spiperone binding sites and the dopamine content of each region was demonstrated, while there were no major difference in KD values among these regions.