Involvement of Inositol Polyphosphates in Neurotermuinal Mechanism and Analysis of the Molecular Mechanism

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C2A and C2B domains of synaptotagmin are functional domains which are involved in exo- and endocytosis of synaptic vesicles, and we have shown that exocytosis is suppressed with the binding of inositol polyphosphates (IP) to C2B domain.In this studies, we investigated about the details of function of both domains using mammalian cells, such as rat supeior cervical ganglion (SCG) neurons or bovine adrenal chromaffin cells, and also investigated about the binding protein to C2B domain.As an another approach, we investigated about the binding protein to the intracellular domain of amyloid precursor protein (APP), because neurotransmission was suppressed by injection of C-terminal peptide of APP into rat SCG neurons.The results revealed that (1) IP inhibited Ca^<2+> -dependent fusion and spontaneous release, but the inhibition disappeared by the treatment with anti-C2B antibody, (2) C2A domain was involved in fusion step of synaptic vesicles as a Ca^<2+> sensor, while C2B domain was involved in both steps of exo- and endocytosis of synaptic vesicles, (3) clathrin assembly protein which is involved in endocytosis bound to C2B domain with high affinity, and this binding was inhibited by IP, (4) novel protein with a molecular mass of 115kDa which binds to the intracellular domain of APP was found in synaptosomes.These results clearly demonstrated that synaptotagmin was a central key molecule which regulates the functions of synaptic vesicles via C2A and C2B domains.Further, it is possible that discover of the novel protein which binds to the intracellular domain of APP contributes to biochemical elucidation for Alzheimer's desease.The studies are now in progress about identification of the binding protein.