Regulation of free calmodulin levels by neuromodulin: neuron growth and regeneration.

Neuromodulin is a neurospecific calmodulin binding protein that is implicated in neurite extension, axonal elongation and long-term potentiation. Yuechueng Liu and Daniel Storm propose that neuromodulin binds and concentrates calmodulin on growth cone membranes and that stimulation of protein kinase C releases high local concentrations of calmodulin in the growth cone. Interactions between released calmodulin and cytoskeleton proteins may affect the polymerization, crosslinking and membrane attachment of cytoskeleton polymers. This local 'softening' of the membrane may be an initial event in filopodia formation and extension.