Роль ендоплазматичної Ca2+-функціональної одиниці у процесах трансдукції сигналу P2Y-рецепторів секреторних клітин слинних залоз личинки дзвінця

Abstract

ІP 3 -dependent Са 2+ -channels inhibitor 2-АPB in low concentrations (1–10 µmol/l) causes increase of stored Са 2+ content in salivary glands of Chironomus plumosus larvae, both incubated as in nominally calcium-free medium and in the medium with physiological Са 2+ concentration. This effect is caused by inhibition of ІP 3 -dependent Са 2+ -channels, decreasing of Ca 2+ -release from endoplasmic reticulum which results in shift of endoplasmic Са 2+ -functional unit equilibrium in the direction of Са 2+ accumulation in the intracellular stores. After incubation of glands with 2-APB in hypercalcium medium decrease of Са 2+ content in secretory cells was observed. Presence of high concentration of 2-APB (20–100 µmol/l) in incubation medium leads to decrease of Са 2+ content in secretory cells independently of Са 2+ concentration. This effect most probably is caused by the inhibition of SERCA Са 2+ -pump, which is a part of endoplasmic Са 2+ -functional unit, decrease of Ca 2+ uptake resulting in shift of equilibrium in direction of release of stored Са 2+ . Application of ATP or ADP in the nominal Ca 2+ -free medium induces a decrease of Са 2+ content in the secretory cells as a result of P2Y-receptors activation. At the same time, presence of 2-APB (10 µmol/l) in nominally Ca 2+ -free medium abolishes the ATP-induced Са 2+ release of Са 2+ , and did not influence ADP-induced decrease of Са 2+ concentration in the secretory cells. According to the obtained data, we assume the presence of two subtypes of Р2Y-receptors in secretory cells of Chironomus plumosus larvae salivary glands. Receptors of the first subtype (P2Y ATP ) have higher affinity to ATP and are coupled with IP 3 -dependent Са 2+ -channels. Activation of endoplasmic Са 2+ -functional unit is a basic mechanism of the signal transduction following activation of this subtype of receptors. Receptors of the second subtype (P2Y ADP ) have higher affinity to ADP and exert their functions through other mechanism. Addition of 2-APB to hipercalcium media abolishes the ATP- and ADP-induced changes in Са 2+ content in glands' tissue due to changes in the integrity of endoplasmic Са 2+ -functional unit. Keywords : 2-АPB, P2Y and P2X, ІP 3 -dependent Са 2+ -channels, Са 2+ -pump of endoplasmic reticulum, endoplasmic Са 2+ -functional unit, exocrine secretory cells.