[The calcium signal in the physiology of the secretory process. I]

The author gives an account of contemporary knowledge and hypotheses on the role of calcium as the second messenger signalizing stimulation of the secretory cell by a specific secretagogue stimulus. The basic structures from which calcium ions are released into the cytosol are the endoplasmatic reticulum, secretory granules and the cell membrane. The author discusses also the importance of mitochondria which act as an intracellular calcium reservoir. An important source of calcium for activation of the secretory process is also the extracellular space. Oscillation of the electric tension of the membrane of the excitable cell which causes temporary opening of the calcium channels participates also in the rise of this ion concentration in the cytosol; in the majority of endocrine systems, however, only in the second stage of the secretory process. In the reparative stage the intracellular reserves are resaturated with calcium. The ratio of the intra- and extracellular source depends probably on the type of secretory cell and the secretagogue stimulus. The author refers to some of her own clinical investigations where it did not prove possible to demonstrate the inhibiting action of calcium current blockers in the secretory process of excitable systems. Based on theoretical findings and hypotheses, she explains the inhibitory action of acute hypercalcaemia on some hormonal functions. In the review attention is paid to the function of calmodulin which is a mediator of the calcium signal and probably the site of interaction of some calciotropic substances.