The purpose of this project has been to study the handling of calcium in neurons especially as it involves the endoplasmic reticulum. The approaches taken include: 1) localization of Ca-binding sites; 2) attempts to localize Ca stores; 3) using the freeze-fracture techniques to compare structure of junctions between ER and surface membrane of neurons with similar junctions in muscle; 4) studying the appearance of the ER with various conditions known physiologically to alter the amount of Ca in the cytoplasm; 5) correlation of the amount of surface membrane involved in subsurface cistern junctions and the prominance of Ca current during action potentials in various neuronal types; and 6) correlation of a pattern of distribution of subsurface cisterns with bursting membrane potential behavior. BIBLIOGRAPHIC REFERENCES: Henkart, M. and Hagiwara, S.: Localization of calcium binding sites associated with the calcium spike in barnacle muscle. J. Mem. Biol. 27: 1-2, 1976. Henkart, M., Landis, D.M.D. and Reese, T.S.: Similarity of junctions between plasma membranes and endoplasmic reticulum in muscle and neurons. J. Cell Biol. 70: 338-347, 1976.