Possible mechanisms involved in the release and modulation of release of neuroactive agents.

Although it is almost universally assumed that exocytosis is the mechanism whereby the release of neuroactive agents is effected, a critical examination of the evidence reveals that other mechanisms may be operative. Possibilities involving gating mechanisms include Na(+), K(+)-ATPase, protein phosphorylation, protein carboxymethylation, the "phosphatidyl inositol effect" and lipid transmethylation. Because of the speed of neurotransmitter release, the more leisurely biochemical cascades are more likely referable to modulation of release rather than functioning in the release process itself.