Evidence for release of copper in the brain: Depolarization‐induced release of newly taken‐up 67 copper

The potential importance of copper (Cu) in neurosecretion can be inferred from the demonstration that extracellular Cu modulates the secretory function of peptidergic neurons (in vitro studies) and from the presence of high Cu concentrations in nerve terminals and secretory vesicles, primarily within the soluble matrix of the latter. We have previously hypothesized that vesicular Cu is released from neurons undergoing exocytosis and that such extracellular Cu plays an important modulatory role in the central nervous system. To test this Cu release hypothesis, rat hypothalami were incubated under in vitro conditions for 1 or 2 hr with 20 nM radiolabeled Cu ( 67 Cu), and then 67 Cu release was stimulated by a depolarizing concentration (60 mM) of K + . K + markedly (P < 0.001) stimulated 67 Cu release in a Ca 2+ ‐dependent manner (stimulated release was 95 fmol/10 min/mg protein after 1 hr 67 Cu loading and 160 after 2 hr). These amounts of released 67 Cu account for about 10% of the total 67 Cu taken up by the tissue. These results indicate that part of the 67 Cu taken up by hypothalamic explants is directed into an intracellular compartment from where it can be released by a Ca 2+ ‐dependent mechanism, thus providing strong support to our hypothesis that release of copper is operative in situ in the brain.