Chorna T. Са2+-transport systems of the secretory cells of Drosophila melanogaster larval salivary glands

Identification of Са2+-transport systems of the secretory cells of Drosophila melanogaster larval salivary glands was carried out in this work. It was shown functional expression of voltage-gated Ca2+-channels in the secretory cells due to the intracellular Ca2+ content changes under the influence of hyperpotassium depolarization and channel inhibitors. We revealed these channels to be sensitive to the verapamil. Interestingly, based on pharmacological properties they are similar to the L-type Ca2+-channels of the epithelial cells of the adult Drosophila melanogaster Malpighian tubules. Different ATP concentrations caused an increase in intracellular Ca2+ level in the secretory cells. This suggests about P2-receptors functioning and a possible role of ATP as a primary messenger in these organs. Submicromolar ryanodine concentrations evoked an elevation in intracellular Ca2+ content in the secretory cells. This could result from its inhibitory effect on the ryanodine-sensitive Ca2+-channels functioning. Itp-r83A, Са-Р60А, olf186-F genes expression was established in the secretory cells by means of reverse transcription and polymerase chain reactions. The expression pattern of the Itp-r83A in Drosophila salivary glands suggests that as in vertebrates the inositol-1,4,5-triphosphate Ca2+-channel plays an important role in Ca2+-signaling of the insect exocrine glands. Based on the Са-Р60А expression we concluded about the endoplasmic reticulum Ca2+-pump functioning in these organs. Elevation of the membranebound Ca2+ level in the gland tissue under the influence of thapsigargin is the functional evidence of this Ca2+-transport system expression in the investigated secretory cells. We identified the olf186-F gene encoding the Orai protein as an essential component of the store-operated Ca2+-channel in the plasma membrane of the secretory cells. To reveal its functional evidence we depleted intracellular Ca2+-stores by thapsigargin and ionomycin. We showed that store-operated Ca2+ entry into these cells was activated after depletion of internal stores by ionomycin and thapsigargin in response to the readmission of external Са2+ ions. Our results confirm about variety of Ca2+-transport systems in the secretory cells of Drosophila melanogaster larval salivary glands and about it involvement in Ca2+-signaling of these organs.