Neuropeptide Y receptors in a protozoaStylonychia mytilus

Radio ligand binding assays(RLBA) were used to study neuropeptide Y (NPY) receptors in a protozoaStylonychia mytilus. The experimental results showed that 2–3 × 10³/mLStylonychia cells incubated in Pringsheim solution which contained³H-NPY could specifically bind³H-NPY and concoraitantly present saturable characteristic. This suggested thatStylonychia possessed some specific binding sites for NPY. Scatchard transformations of binding assay for the NPY receptors at 25°C are compatible with the specific activity of 42. 47 fmol/10³ cells and the binding equilibrium constant of 0. 113 nmol/L. The data of¹²⁵I-NPY binding assay to the membrane protein extract ofStylonychia indicated that there was a significant difference between the amount of total bound and nonspecific bound of¹²⁵I-NPY. This result indicated that NPY receptors were probably localized mainly on the cell membrane.