Intracellular Ca2+ channel immunoreactivity in neuroendocrine axon terminals

The concentration of neuroendocrine terminals in the neurohgpophysis facili tates the identification and localization of Ca2+ channel subtypes near neu roendocrine release sites. Immunoblots of rat neurohypophysial tissue ident ified the alpha(1)1.3, alpha(1)2.1, alpha(1)2.2, and alpha(1)2.3 Ca2+ chann el subunits, Immunofluorescence staining of axon terminal plasma membranes mas weak, suggesting that Ca2+ channels are dispersed. This contrasts with the highly punctate alpha(1)2.2 immunoreactivity in bovine chromaffin cells ; the neurohypophysial terminals mall therefore lack the specialized releas e zones found in those cells. Immunofluorescence and immunogold labeling id entify dense core granule-like structures in the terminal cytoplasm contain ing multiple Ca2+ channel types, Ca2+ channels in internal membranes may pl ay an important role in channel targeting and distribution in neuroendocrin e cells. (C) 2000 Federation of European Biochemical Societies. Published b y Elsevier Science B.V. All rights reserved.