title: Inositol 1,4,5-trisphosphate-triggered Ca2+ release from bovine adrenal medullary secretory vesicles.
abstract: The effect of inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) and calcium ionophore A23187 on Ca2+ release from bovine adrenal medullary secretory vesicles and microsomes was examined. Ins(1,4,5)P3 released 3.5 nmol of Ca2+/mg protein from secretory vesicles and 1.5 nmol of Ca2+/mg protein from microsomes as measured by a Ca2(+)-selective electrode. However, A23187 promoted Ca2+ uptake into vesicles while releasing Ca2+ from microsomes. Ins(1,4,5)P3-induced Ca2+ release from secretory vesicles was rapid, but the released Ca2+ was absorbed within 3 min during which the Ins(1,4,5)P3-releasable pools were refilled. The in situ calcium content of secretory vesicle measured by atomic absorption spectrometry was 112 +/- 6.3 nmol/mg protein indicating the potential importance of secretory vesicles as an intracellular Ca2+ store. The high Ca2(+)-buffering capacity of secretory vesicles is presumed to be due to the high Ca2(+)-binding capacity of chromogranin A, the major intravesicular protein, which has calsequestrin-like properties.
authors.affiliation: Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas 75235-9041.
authors.forename: S H
authors.initials: SH
authors.lastname: Yoo
authors.forename: J P
authors.initials: JP
authors.lastname: Albanesi
mesh_terms: D000313:Adrenal Medulla / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002395:Catecholamines / Q000378:metabolism; D002417:Cattle; D002837:Chromaffin Granules / Q000187:drug effects / Q000378:metabolism*; D002838:Chromaffin System / Q000378:metabolism*; D004299:Dopamine beta-Hydroxylase / Q000378:metabolism; D005952:Glucose-6-Phosphatase / Q000378:metabolism; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology*; D007700:Kinetics; D008861:Microsomes / Q000187:drug effects / Q000378:metabolism; D013054:Spectrophotometry, Atomic
chemical_list: D002395:Catecholamines; D015544:Inositol 1,4,5-Trisphosphate; D004299:Dopamine beta-Hydroxylase; D005952:Glucose-6-Phosphatase; D002118:Calcium