Immunocytochemical Localization of Calmodulin

Antisera to calmodulin, a Ca"-dependent modulator protein, and a heat-labile calmodulin-binding protein have been used to localize these proteins in mouse caudate-putamen. The two proteins appear to be located at identical sites in this brain area . At the light microscopic level, calmodulin and calmodulin-binding protein are found within the cytoplasm and processes of large cells . At the electron microscopic level the proteins are associated with neuronal elements only, primarily at postsynaptic sites within neuronal somata and dendrites . Within the dendrites the immunocytochemical label is associated predominantly with the postsynaptic density and dendritic microtubules . These results are in accord with recent biochemical and immunohistochemical studies of calmodulin in brain and in dividing cells . Thus, calmodulin and the heat-labile calmodulin-binding protein may play a role in the nervous system at the site of neurotransmitter action and at the level of microtubular function .