We showed previously that Ca2+ and the Ca2+-binding protein, calmodulin, can act together to displace the GTP-binding protein, Rab3A, from macaque brain prefrontal cortex synaptic vesicle membranes. The physiological relevance of this new observation remains to be determined, but studies of whole rat brain synaptosomes and their homogenates by other investigators have raised the possibilities that a special mechanism may increase the local concentration of Ca2+ calmodulin in activated nerve terminals and that Rab3A may dissociate from synaptic vesicles during the process of neurotransmitter secretion. Last year we studied depolarized synaptosomes from the prefrontal cortex of macaque brains in an attempt to reproduce the findings that had been made in studies of rat brain preparations. We were able to prepare macaque synaptosomes that could show a dramatic neurosecretory response, but when we attempted to homogenize them, the depolarized synaptosomes proved to be unexpectedly stable. We therefore discontinued the experiments and published our findings in the Journal of Biological Chemistry.
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