Calcium-Binding Proteins in Synaptic Vesicle Exo- and Endocytosis in Somatic Motor Nerve Endings of the Earthworm Lumbricus terrestris

Using fluorescence microscopy, we studied the involvementof Ca²⁺-binding proteins in the exo-endocytoticvesicular cycle of quantal neurotransmitter release at the somaticneuromuscular junction of the earthworm Lumbricusterrestris. Inhibition of calcineurin, calmodulin, andCa²⁺/calmodulin-dependent protein kinasesled to an enhancement of synaptic vesicle endocytosis. Blockingthe phosphorylation of synaptic calcium-binding proteins boostedvesicular endocytosis, increased the size of the total vesicularpool, and accelerates synaptic vesicle turnover. It can be concludedthat calcium modulation of synaptic vesicle exo- and endocytosisin the motor nerve endings of evolutionarily primitive somatic musclesof annelids occurs with the involvement of calcineurin, calmodulinand Ca²⁺/calmodulin-dependent proteinkinases.