title: Calcium-dependent exocytosis of atrial natriuretic peptide from astrocytes.
abstract: Astrocytes are non-neuronal cells in the CNS, which, like neurons, are capable of releasing neuroactive molecules. However, the mechanism of release is ill defined. In this study, we investigated the mechanism of release of atrial natriuretic peptide (ANP) from cultured cortical astrocytes by confocal microscopy. To study the discharge of this hormone, we transfected astrocytes with a construct to express pro-ANP fused with the emerald green fluorescent protein (ANP.emd). The transfection of cells with ANP.emd resulted in fluorescent puncta in the cytoplasm that represent secretory organelles. If ANP is released by exocytosis, in which the vesicle fuses with the plasma membrane, then the total intensity of the green fluorescing probe should decrease, whereas the vesicle membrane is incorporated into the plasma membrane. To monitor exocytosis, we labeled the membrane with the fluorescent styryldye FM 4-64, a reporter of cumulative exocytosis. The application of ionomycin to elevate cytoplasmic [Ca(2+)] increased the fluorescence intensity of FM 4-64, whereas that of ANP.emd decreased. These effects were not observed in the absence of extracellular Ca(2+), suggesting that ANP is released by regulated Ca(2+)-dependent exocytosis from astrocytes.
authors.affiliation: Laboratory of Neuroendocrinology-Molecular Cell Physiology, Institute of Pathophysiology, Medical Faculty, University of Ljubljana, 1000 Ljubljana, Slovenia.
authors.forename: Mojca
authors.initials: M
authors.lastname: Krzan
authors.forename: Matjaz
authors.initials: M
authors.lastname: Stenovec
authors.forename: Marko
authors.initials: M
authors.lastname: Kreft
authors.forename: Tina
authors.initials: T
authors.lastname: Pangrsic
authors.forename: Sonja
authors.initials: S
authors.lastname: Grilc
authors.forename: Philip G
authors.initials: PG
authors.lastname: Haydon
authors.forename: Robert
authors.initials: R
authors.lastname: Zorec
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009320:Atrial Natriuretic Factor / Q000235:genetics / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D005456:Fluorescent Dyes; D017930:Genes, Reporter; D007476:Ionophores / Q000494:pharmacology; D051381:Rats; D014162:Transfection
chemical_list: D005456:Fluorescent Dyes; D007476:Ionophores; D009320:Atrial Natriuretic Factor; D002118:Calcium