title: Properties of Ca(2+)-dependent exocytosis in cultured astrocytes.
abstract: Astrocytes, a subtype of glial cells, have numerous characteristics that were previously considered exclusive for neurons. One of these characteristics is a cytosolic [Ca2+] oscillation that controls the release of the chemical transmitter glutamate and atrial natriuretic peptide. These chemical messengers appear to be released from astrocytes via Ca(2+)-dependent exocytosis. In the present study, patch-clamp membrane capacitance measurements were used to monitor changes in the membrane area of a single astrocyte, while the photolysis of caged calcium compounds by a UV flash was used to elicit steps in [Ca2+]i to determine the exocytotic properties of astrocytes. Experiments show that astrocytes exhibit Ca(2+)-dependent increases in membrane capacitance, with an apparent Kd value of approximately 20 microM [Ca2+]i. The delay between the flash delivery and the peak rate in membrane capacitance increase is in the range of tens to hundreds of milliseconds. The pretreatment of astrocytes by the tetanus neurotoxin, which specifically cleaves the neuronal/neuroendocrine type of SNARE protein synaptobrevin, abolished flash-induced membrane capacitance increases, suggesting that Ca(2+)-dependent membrane capacitance changes involve tetanus neurotoxin-sensitive SNARE-mediated vesicular exocytosis. Immunocytochemical experiments show distinct populations of vesicles containing glutamate and atrial natriuretic peptide in astrocytes. We conclude that the recorded Ca(2+)-dependent changes in membrane capacitance represent regulated exocytosis from multiple types of vesicles, about 100 times slower than the exocytotic response in neurons.
authors.affiliation: Medical Faculty, University of Ljubljana, Ljubljana, Slovenia.
authors.forename: Marko
authors.initials: M
authors.lastname: Kreft
authors.forename: Matjaz
authors.initials: M
authors.lastname: Stenovec
authors.forename: Marjan
authors.initials: M
authors.lastname: Rupnik
authors.forename: Sonja
authors.initials: S
authors.lastname: Grilc
authors.forename: Mojca
authors.initials: M
authors.lastname: Krzan
authors.forename: Maja
authors.initials: M
authors.lastname: Potokar
authors.forename: Tina
authors.initials: T
authors.lastname: Pangrsic
authors.forename: Philip G
authors.initials: PG
authors.lastname: Haydon
authors.forename: Robert
authors.initials: R
authors.lastname: Zorec
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D009320:Atrial Natriuretic Factor / Q000378:metabolism; D001683:Biological Clocks / Q000187:drug effects / Q000502:physiology; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002450:Cell Communication / Q000187:drug effects / Q000502:physiology; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D025802:Electric Capacitance; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D018698:Glutamic Acid / Q000378:metabolism; D008565:Membrane Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D009474:Neurons / Q000378:metabolism; D050683:R-SNARE Proteins; D051381:Rats; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology; D013744:Tetanus Toxin / Q000494:pharmacology; D022161:Transport Vesicles / Q000378:metabolism
chemical_list: D008565:Membrane Proteins; D050683:R-SNARE Proteins; D013744:Tetanus Toxin; D018698:Glutamic Acid; D009320:Atrial Natriuretic Factor; D002118:Calcium