STORE-OPERATED Ca2+-ENTRY INTO THE SECRETORY CELLS OF DROSOPHILA MELANOGASTER LARVAL SALIVARY GLANDS

Abstract

Confocal microscopy enabled the identification of store-operated Ca²⁺ entry in the sec­retory cells of Drosophila melanogaster larval salivary glands, which expresses Ca²⁺ sensor G-CaMP1.6. To release Са²⁺ from intracellular stores, we used Са²⁺ ionophore ionomycin and endoplasmic reticulum Са²⁺-pump inhibitor thapsigargin. Addition of these compounds to the Са²⁺-free medium caused slight and non-transient elevation of the cytosolic Са²⁺ concentration in the secretory cells. After an increase of Са²⁺ concentration at 2 mmol/l, a significant increase in cytosolic Са²⁺ level appeared in both cases. Although under the use of ionomycin, an increase of cytosolic Са²⁺ was transient in all cases, Са_e²⁺-induced Са²⁺-transients from different cells of investigated gland’s region were synchronous, and determined by activation of store-operated Са²⁺ entry as well as by its entry from extracellular medium under the ionophoretic exchange. In case of emptying stores by thapsigargin, an increase of extracellular Са²⁺ concentration induced in part of the cells, fast transients of cytosolic Са²⁺, in some part – slow primary transients, which changes by non-transient elevation of cytosolic Са²⁺ level, and in another part – only non-transient increase of cytosolic Са²⁺ level. Such differen­ces of Са_e²⁺-induced Са²⁺-transients in different cells is determined, perhaps, by the fact that their generation involved only store-operated Са²⁺-channels as far as other Са²⁺-transport systems of plasma membrane and intracellular organelles.