Phosphorylation of synapsin I and MARCKS in nerve terminals is mediated by Ca2+ entry via an Aga‐GI sensitive Ca2+ channel which is coupled to glutamate exocytosis

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Abstract
Ca2+ entry is a prerequisite for both exocytosis and the phosphorylation of synapsin I and MARCKS proteins in mammalian cerebrocortical synaptosomes. The novel spider toxin Aga‐GI completely blocks KCl‐evoked glutamate exocytosis but only partially inhibits KCl‐evoked cytoplasmic Ca2+ elevations, thus revealing at least two pathways for KCl‐induced Ca2+ entry. Aga‐GI completely attenuates KCl‐induced phosphorylation of synapsin I and MARCKS proteins. We therefore conclude that both exocytosis and the phosphorylation of synapsin I and MARCKS proteins are specifically coupled to Ca2+ entry via a subset of voltage dependent Ca2+ channels at the nerve terminal which are sensitive to Aga‐GI.