title: Effects of media of low osmolarity on the dense bodies of human platelets.
abstract: Exposure of human platelets to buffer at 30 milliosmoles (mOs) caused marked swelling of the cells (a volume increase of almost 300% as estimated from electronic sizing) without a statistically significant loss of dense bodies or a change in the measured diameter of the dense-body core (as examined electron-microscopically in air-dried whole mounts). Even biochemically isolated dense bodies maintained the integrity of their electron-opaque cores in 30 mOs buffer. However, exposure of platelets to 30 mOs buffer reduced the platelet content of cytoplasmic 14C-labeled nucleotides and the vesicular content of [3H]5-hydroxytryptamine (5-HT) by 90%. It thus seems likely that the dense-body membrane displays a sufficiently low permeability to water to prevent swelling and dissolution of the core, but that exposure to hypotonic media allows stored 5-HT to cross the vesicular membrane. Impermeability of this membrane to 5-HT under normal conditions may, therefore, play an important role in the maintenance of vesicular 5-HT stores, rather than the presence of an intact dense-body core. The data also suggest that an "osmotic lysis" or "chemiosmotic" model of secretion may not account for the exocytotic release of human platelet dense bodies.
mesh_terms: D001792:Blood Platelets / Q000166:cytology*; D003470:Culture Media; D006801:Humans; D009994:Osmolar Concentration; D010976:Platelet Count; D012701:Serotonin / Q000097:blood
chemical_list: D003470:Culture Media; D012701:Serotonin