Autoradiographic characterization of [3H]inositol (1,4,5) trisphosphate and [3H]inositol (1,3,4,5) tetrakisphosphate binding sites in human brain

Autoradiographic techniques were used to investigate the characteristics of tritiated inositol(1,4,5)trisphosphate ([3H]IP3) and inositol (1,3,4,5)tetrakisphosphate ([3H]IP4) binding to human brain. In brain sections [3H]IP3 exhibited a two-site binding with Kd values of 87 nM and 9.3 μM respectively for the higher and lower affinity sites. [3H]IP4 also bound to two sites with Kd values of 43 nM and 1.4 μM, respectively. With the conditions fixed in this study, [3H]IP3 and [3H]IP4 autoradiography in the cortex, caudate, hippocampus and cerebellum were performed. The most prominent [3H]IP3 binding among these regions was found in the cerebellum, particularly in the molecular layer. Within the hippocampus, the subiculum and the CA1 region showed much more prominent binding than the other subfields. [3H]IP4 binding was fairly homogeneous in the regions studied, with the exception of a slightly higher binding in the molecular layer of the cerebellum.