Role for microsomal Ca storage in mammalian neurones?

Alterations in the intracellular concentration of calcium ions ([Ca 2+ ] i ) are increasingly being found to be associated with regulatory functions in cells of all kinds. In muscle, an elevation of [Ca 2+ ] i , is the final link in excitation–contraction coupling 1–3 while at nerve endings and in secretory cells, similar rises in [Ca 2+ ] i , are thought to mediate exocytosis 4,5 . The discovery of calcium-activated ion channels 6,7 indicated a role for intracellular calcium in the regulation of membrane excitability. Calcium transients associated with either intracellular release or the inward movement of Ca 2+ across the membrane have been recorded in molluscan neurons 8,9 and more recently in neurones of bullfrog sympathetic ganglia 10 . Here, we report the first recordings of calcium transients in single mammalian neurones. In these experiments we have found that the methylxanthine, caffeine, causes the release of calcium from a labile intracellular store which can be refilled by Ca 2+ entering the cell during action potentials.