Protein Phosphorylation and Dephosphorylation in Isolated Nerve Terminals (Synaptosomes)

Nerve terminal depolarization leads to Ca²⁺ influx and the exocytotic release of neurotransmitters (Jessell and Kandel, 1993; Kelly, 1993). Elucidation of the regulatory influences on this primary function of the nerve terminal is of fundamental importance in understanding synaptic function. Posttranslational modification of proteins by phosphorylation /dephosphorylation is a means of altering the characteristics of a protein and thus represents a key molecular mechanism through which neuronal function can be regulated (Greengard, 1987; Walaas and Greengard, 1991). The aim of this chapter is to provide a working knowledge of the isolated nerve terminal preparation (synaptosomes) as a model for studying protein phosphorylation changes that are specific to the presynaptic digit of the synapse. Each section will briefly review the literature to provide a historical overview of how present working paradigms have been derived. Experimental details will be provided, with appropriate examples, to enable the investigator to analyze a putative regulatory presynaptic phosphoprotein to increasing molecular detail.