THE ROLE OF INTRACELLULAR ORGANELLES IN Ca2+-HOMEOSTASIS IN SECRETORY CELLS OF THE LACRIMAL GLAND

Abstract

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.