Characteristics of 3H-substance P binding sites in rat brain membranes

Binding characteristics of 3H-Substance P (SP) were studied with rat brain membranes using a method applied to peripheral tissues. This method was well applicable to central nervous system (CNS) tissues. The results in the present study indicate that specific 3H-SP binding reaches a plateau only after 20 minutes of incubation, and the binding sites are saturable at a relatively low concentration of 3H-SP. Scatchard analysis of specific binding data reveals a single class of binding sites with a high affinity and a low density in rat brain membranes. A Hill plot of the displacement curve of 3H-SP with unlabelled SP showed no indication for cooperativity (nH . 0.83). The relative potencies of binding of various SP fragments at 3H-SP binding sites were fairly parallel to the length of the C-terminal fragments. Neurotransmitters not structurally related to SP produced no effect on 3H-SP binding even when used at micromolar concentrations