Концепція Cа2+-функціональних одиниць у застосуванні до секреторних клітин слинних залоз личинки Chironomus plumosus

Abstract

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