title: Reversible condensation of mast cell secretory products in vitro.
abstract: We have investigated the mechanisms responsible for the condensation and decondensation of secretory products that occur in mast cell secretion. We show here that the hydrated matrix of an exocytosed secretory granule can be recondensed to its original volume by exposure to acidic solutions containing histamine at concentrations that mimic those found in vivo. Recondensation by acidic histamine began in the range of 1-10 mM with a dose response curve that was accurately predicted by a Hill type equation with four highly cooperative binding sites and a half maximum concentration of [Hi++] = 3.9 mM. Recondensation by histamine showed a sigmoidal dependency on pH (critical range pH 5.5-6.5) and was fully reversible. These experiments suggest that histamine, possibly by binding to anionic sites in the protein-heparin complex of the granule matrix, triggers a change in the polymeric structures of the granule matrix from an extended coil to a collapsed globular state. This may be a useful model for understanding the condensation of secretory products into dense core granules and their subsequent decondensation upon exocytosis.
authors.affiliation: Department of Physiology and Biophysics, Mayo Clinic, Rochester, Minnesota 55905.
authors.forename: J M
authors.initials: JM
authors.lastname: Fernandez
authors.forename: M
authors.initials: M
authors.lastname: Villalón
authors.forename: P
authors.initials: P
authors.lastname: Verdugo
mesh_terms: D000818:Animals; D002122:Calcium Chloride / Q000494:pharmacology; D003594:Cytoplasmic Granules / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D005089:Exocytosis; D006632:Histamine / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007700:Kinetics; D015636:Magnesium Chloride / Q000494:pharmacology; D008407:Mast Cells / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D008815:Mice, Inbred Strains; D011189:Potassium Chloride / Q000494:pharmacology; D012965:Sodium Chloride / Q000494:pharmacology
chemical_list: D015636:Magnesium Chloride; D012965:Sodium Chloride; D011189:Potassium Chloride; D006632:Histamine; D002122:Calcium Chloride