SYNAPSIN-I REGULATES GLUTAMATE RELEASE FROM RAT-BRAIN SYNAPTOSOMES

Introduction of the dephosphorylated form of synapsin I into rat brain synaptosomes using freeze-thaw (transient) permeabilization significantly decreased the K+-induced release of glutamate. In contrast, introduction of synapsin I that had been phosphorylated by Ca2+/calmodulin-dependent protein kinase II was without effect on glutamate release. Addition of dephosphosynapsin I after freeze-thaw treatment also had no effect. Thus, the action of synapsin I was dependent on the phosphorylation state of synapsin I and on its entry into the synaptosomes. Our results implicate synapsin I as an important component in the regulation of neurotransmitter release in the mammalian nervous system.