D‐[35S(U)]Inositol 1,4,5‐trisphosphorothioate, a novel radioligand for the inositol 1,4,5‐trisphosphate receptor Complex binding to rat cerebellar membranes

Abstract
D‐[35S(U)]mya‐inositol 1,4,5‐trisphosphorothioate ([35S]InsPS3), a synthetic, metabolically stable analogue of inositol 1,4,5‐trisphosphate (InsP3) binds with high affinity (Ka 58.6±9.1 nM) to rat cerebellar revealing a high density of specific binding sites (D max 21.5±2.1 pmol/mg of protein). Comparison with [3H]InsP3 binding reveals a higher density of sites labelled by [35S]InsPS3 and complex competition curves for displacement of specific [35S]insPS3 by InsP3. The results suggests that [35S]InsPS3 labels two sites in rat cerebellar membranes with equal affinity: the InsP3 receptor and a site that displays low affinity for InsP3.