The Signaling Function of Calcium and Its Regulation
In the course of evolution Ca has become a signaling agent of universal significance, which controls a large number of cellular functions: prominent among them are the synthesis and release of hormones, muscle and non-muscle motility, and a multiplicity of membrane-linked processes (see Carafoli, 1987, for a recent comprehensive review). It is self evident that the signaling function of Ca demands its maintenance within cells at a very low free concentration, and mechanisms to efficiently modulate it in the cell compartments where the targets of the signaling function are located. Other signaling agents are regulated within cells by biosynthesis and breakdown. Since this is impossible in the case of Ca, evolution has selected an entirely different control mechanism, i.e., the reversible complexation by specific proteins, which are either soluble, organized in non membranous structures, or intrinsic to membranes. These proteins “buffer” intracellular Ca at a concentration which is at least 10,000 fold lower than in the external spaces. The functional cycle of cells requires both short and long term regulation of Ca. The rapid and precise modulation is performed by intracel1ular Ca binding proteins but also (in fact mostly, see below) by high Ca affinity membrane intrinsic proteins. The Ca-filtering function of the plasma membrane, which depends on the operation of membrane-intrinsic Ca binding proteins, is responsible for the long term maintenance of the Ca gradient between cells and medium.
KeywordsVanadate Pyruvate Caffeine Cytosol Hydroxyapatite
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- Carafoli, E., 1982, The transport of calcium across the inner membrane of mitochondria, in: “Membrane Transport of Calcium”, E. Carafoli, ed., Academic Press, London, pp 109.Google Scholar
- Carafoli, E., 1982, Membrane transport and the regulation of the cell calcium levels, in: “Pathophysiology of Shock, Anoxia, and Ischemia”, R.A. Cowley, and B.F. Trump, eds., Williams and Wilkins, pp 95.Google Scholar
- Fabiato, A., and Fabiato, F., 1975, Contractions induced by a calcium triggered release of calcium from the sarcoplasmic reticulum of single skinned cardiac cells, J. Physiol., 249: 457.Google Scholar
- Fleckenstein, A., 1973, Calcium antagonism in heart and smooth muscle, John Wiley, New York.Google Scholar
- Krause, K.H., Volpe, P., Zorzato, F., Hashimoto, S., Pozzan, T., Meldolesi, J., and Lew, P.D., 1987, Calciosomesi evidence for a new type of organelle regulating intracellular Ca, Seventh Intern. Washington Spring Symposium, Abstract 64.Google Scholar
- Schatzmann, H., 1982, The calcium pump of erythorcytes and other animal cells, in “Membrane Transport of Calcium”, E. Carafoli, ed., Academic Press, London, pp 41.Google Scholar