Cа2+-functional units conception concerning to secretory cell of Chironomus plumosus larvae salivary gland

• Main Author: V. V. Manko
• Format: Article
• Language: English
• Published: Львівський національний університет імені Івана Франка 2008-09-01
• Series: Біологічні студії
• Subjects: ca2+-functional unit; na+-ca2+ exchanger; ca2+-pump; voltage-operated ca2+-channels; insp3r; ryr; ca2+- uniporter; secretory cells
• Online Access: http://publications.lnu.edu.ua/journals/index.php/biology/article/view/497

On the basis of analysis of experimental data received during investigation of Ca2+-transporting systems of secretory cells of salivary glands of Chironomus plumosus larvae, a conception of Ca2+-functional units has been proposed. According to this conception, Ca2+-functional unit is an abstract model which consists of with active and passive Ca2+-transporting systems and cellular membrane providing Ca2+ cations compartmentalisation. There are type I (active and passive transporting systems located in the same membrane) and type II (active and passive transporting systems located in different membranes of the same cell) Ca2+-functional units. In both cases, Ca2+-functional unit is not a static structure, but a dynamic one, that ensure proper [Ca2+] support in cytosol. It may be in three states: 1) resting state the is characterised by a dynamic balance between the influx and efflux of Ca2+ flow; 2) active state of Ca2+ influx (regarding cytosol) prevailing over the efflux; 3) inactive state (oppositely, Ca2+ efflux prevailing over its influx). Factors which due to direct positive or negative feedback are supporting Ca2+-transporting systems transition between different states, are Ca2+ cations, since the activity of majority of Ca2+-transporting systems depends on cytosol concentration of Ca2+. Endoplasmic Ca2+-functional unit of investigated secretory cells combines Ca2+-pump of endoplasmic reticulum, lnsP3Rs and RyRs. As a result of 1) ryanodine adding to incubatory medium of glands in submicromolar concentration causes Ca2+ content increasing in their tissue; 2) lnsP3Rs stimulation prevents simultaneous RyRs stimulation or contrariwise; 3) heparin causes Ca2+ content increasing in gland tissue, treated with saponin, but only in ryanodine presence in medium in concentration activating RyRs. Ca2+-functional unit of plasma mambrane are formed by voltage-operated Ca2+-channels, Na+-Ca2+ exchanger and Ca2+-pump of plasma membrane. That assumption is based on the fact that between the voltage-operated Ca2+-channel and Na+-Ca2+ exchanger, from one side, and Na+-Ca2+ exchanger and Ca2+-pump of plasma membrane, from the other side, tight functional links are existing even in case of intracellular perfusion. To some extent, condition of this Ca2+-functional unit are defined by Na+-Ca2+ exchange dependence on Na+-K+ pump activity. Its peculiar feature is also a dependence on membrane potential level, not only on cytosolic [Ca2+]. Distinct Ca2+-transporting systems may be a part of several Ca2+-functional units. Endoplasmic-mitochondrial Ca2+-functional unit consists of Ca2+-release channels of endoplasmic reticulum and mitochondrial Ca2+-uniporter, so far as influence of ryanodine and ruthenium red, and also lnsP3 and ruthenium red under the condition of their combination in incubation medium with Ca2+ content of salivary glands tissue is not additive. Postulated conception could be positioned as a working hypothesis for identification of the role of different Ca2+-transporting systems in coordination of Ca2+-signalling in different cells other than secretory cells of exocrine glands.