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It is known that different Ca2+-transport systems make distinct contribution to the formation of Ca2+-signal in various secretory cells. In recent years there has been a significant increase in interest in study of the lacrimal glands functioning. However, the results of study of the Ca2+-signalling in lacrimal gland have not yet been summarized in the literature. This review is devoted to analysis of functioning of Ca2+-transport system of secretory cells in the rat exorbital lacrimal gland. IP3Rs in exorbital lacrimal gland cells were effectively inhibited by 2-APB (10 μM) and activated by IP3 (2 μM), as well as by cholinomimetics, carbacholine (10 μM) and purine receptor agonists, ATP (1 mM). Signaling pathways activated by P2Y-receptors in the lacrimal gland secretory cells were partially mediated by IP3R activation. RyRs of lacrimal gland secretory cells were activated by Ca2+ and low concentrations of ryanodine (0,05–1 μM). Simultaneous activation of RyRs and IP3Rs in these cells caused Ca2+ release from the same store. Ca2+ mobilization from the intracellular stores induced by carbacholine (10 μM) or thapsigargin (1 μM) caused store-operated Ca2+ entry in secretory cells of the studied glands, which was partially inhibited by 2-APB. SERCA of exorbital lacrimal gland cells was efficiently inhibited by eosin Y (5–10 μM) and by thapsigrgin (1 μM). In contrast to permeabilized cells, the Ca2+ content in intact cells did not change under the influence of eosin Y (5–20 μM), indicating the inhibition of PMCA. Ca2+-ATPase activity of permeabilized cells of studied glands depended on the incubation time, the substrate amount and Ca2+ concentration in the incubation medium. Mitochondrial Ca2+-uniporter of lacrimal gland secretory cells was inhibited by ruthenium red (10 μM). Effects of ryanodine and ruthenium red on the Ca2+ content in cells were statistically significantly non-additive. Furthermore, ryanodine at concentrations of 1–3 μM caused a dose-dependent decrease in the respiration rate of the studied cells and this effect persisted after cells preincubation with ruthenium red or thapsigargin. This suggests that in addition to the endoplasmic reticulum RyRs activation, ryanodine inhibited the Ca2+ transport to the mitochondrial matrix, which was insensitive to the ruthenium red.

The role of intracellular organelles in Ca2+-homeostasis in secretory cells of the lacrimal gland