In salivary glands secretory cells of Chironomus plumosus larvae IP3Rs, RyRs and SERCA are components of endoplasmic Ca2+-functional unit (Manko, 2008; 2011). According to the results of our previous studies (Velykopolska, Manko, 2009) activation of P2Y-receptors of the investigated cells leads to activation of the unit, causing release of Ca2+ from endoplasmic reticulum store. Mechanism of intracellular signal transduction, induced by a particular P2Y-receptor (P2YATP) activation with exogenous ATP, is based on activation of IP3Rs. However the role of RyRs in endoplasmic Ca2+-functional unit activation at ATP/ADP-induced signal transduction is not elucidated. That is why we wanted to investigate this important issue.

In the present study investigation of P2-receptors activation interaction with RyRs salivary glands secretory cells of Chironomus plumosus larvae’ was performed. The content of stored Ca2+ was determined as fluorescence intensity of Ca2+-chlortetracycline complex. Ryanodine at 10 nM was shown to induce Ca2+ release from stores, whereas at 500 nM it caused accumulation of Ca2+. In the following experiments we used activating concentration of ryanodine – 10 nM. To activate P2-receptors we used ATP or ADP at the concentration of 100 μM. Effects of P2-receptor agonists ATP and ADP were similar: in nominally Ca2+-free medium the content of stored Ca2+ decreased, while at the physiological [Ca2+] – it did not change. Decrease of stored Ca2+ content caused by the activation of RyRs was more prominent than at purinergic receptors activation. Adding ATP into Ca2+-free incubatory solution did not augment action of ryanodine, while at the presence of Ca2+ simultaneous ATP and ryanodine application potentiated Ca2+-release from store. We suggest that in this case potentiation of Ca2+-release from store occurs due to the simultaneous activation of various components of endoplasmic Ca2+-functional unit – IP3Rs and RyRs. At simultaneous action of ADP and ryanodine in nominally Ca2+-free medium decrease of stored Ca2+ was not observed, and at the physiological [Ca2+] its content in stores even increased above control values.

We assume that the increase of stored Ca2+ at simultaneous action of ADP and ryanodine is based on the inhibition of RyRs, causing inactivation of endoplasmic Ca2+- functional unit. The peculiarities of simultaneous action of ADP and ryanodine support the hypothesis that in secretory cells of salivary glands of Ch. plumosus larvae various subtypes P2Y-receptor (P2YATP and P2YADP) are functioning, activation of which initiates various pathways of intracellular signal transduction. At simultaneous activation of P2YATP and RyRs the activity of endoplasmic Ca2+-functional unit increases. Simultaneous activation of P2YADP and RyRs, however, inhibits the activity of the unit.

Keywords: P2Y, RyRs, endoplasmic Са2+-functional unit

Full text: PDF (Ukr) 210K