AUTORADIOGRAPHIC CHARACTERIZATION OF [H-3] INOSITOL(1,4,5)TRISPHOSPHATE AND [H-3] INOSITOL(1,3,4,5)TETRAKISPHOSPHATE BINDING-SITES IN HUMANBRAIN

Autoradiographic techniques were used to investigate the characteristi cs of tritiated inositol(1,4,5)trisphosphate ([H-3]IP3) and inositol ( 1,3,4,5)tetrakisphosphate ([H-3]IP4) binding to human brain. In brain sections [H-3]IP3 exhibited a two-site binding with K-D values of 87 n M and 9.3 mu M respectively for the higher and lower affinity sites. [ H-3]IP4 also bound to two sites with K-D values of 43 nM and 1.4 mu M, respectively. With the conditions fixed in this study, [H-3]IP3 and [ H-3]IP4 autoradiography in the cortex, caudate, hippocampus and cerebe llum were performed. The most prominent [H-3]IP3 binding among these r egions was found in the cerebellum, particularly in the molecular laye r. Within the hippocampus, the subiculum and the CA1 region showed muc h more prominent binding than the other subfields. [H-3]IP4 binding wa s fairly homogeneous in the regions studied, with the exception of a s lightly higher binding in the molecular layer of the cerebellum.