title: Calcium dependencies of regulated exocytosis in different endocrine cells.
abstract: Exocytotic machinery in neuronal and endocrine tissues is sensitive to changes in intracellular Ca(2+) concentration. Endocrine cell models, that are most frequently used to study the mechanisms of regulated exocytosis, are pancreatic beta cells, adrenal chromaffin cells and pituitary cells. To reliably study the Ca(2+) sensitivity in endocrine cells, accurate and fast determination of Ca(2+) dependence in each tested cell is required. With slow photo-release it is possible to induce ramp-like increase in intracellular Ca(2+) concentration ([Ca(2+)](i)) that leads to a robust exocytotic activity. Slow increases in the [Ca(2+)](i) revealed exocytotic phases with different Ca(2+) sensitivities that have been largely masked in step-like flash photo-release experiments. Strikingly, in the cells of the three described model endocrine tissues (beta, chromaffin and melanotroph cells), distinct Ca(2+) sensitivity 'classes' of secretory vesicles have been observed: a highly Ca(2+)-sensitive, a medium Ca(2+)-sensitive and a low Ca(2+)-sensitive kinetic phase of secretory vesicle exocytosis. We discuss that a physiological modulation of a cellular activity, e.g. by activating cAMP/PKA transduction pathway, can switch the secretory vesicles between Ca(2+) sensitivity classes. This significantly alters late steps in the secretory release of hormones even without utilization of an additional Ca(2+) sensor protein.
authors.affiliation: Institute of Physiology, Faculty of Medicine, University of Maribor, Maribor, Slovenia.
authors.forename: J
authors.initials: J
authors.lastname: Dolenšek
authors.forename: M
authors.initials: M
authors.lastname: Skelin
authors.forename: M S
authors.initials: MS
authors.lastname: Rupnik
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D055098:Endocrine Cells / Q000378:metabolism*; D005089:Exocytosis; D006801:Humans; D052139:Intracellular Calcium-Sensing Proteins / Q000378:metabolism; D007700:Kinetics; D015290:Second Messenger Systems; D022142:Secretory Vesicles / Q000378:metabolism*
chemical_list: D052139:Intracellular Calcium-Sensing Proteins; D002118:Calcium