Effects of media of low osmolarity on the dense bodies of human platelets.
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.
D001792:Blood Platelets / Q000166:cytology*; D003470:Culture Media; D006801:Humans; D009994:Osmolar Concentration; D010976:Platelet Count; D012701:Serotonin / Q000097:blood
D003470:Culture Media; D012701:Serotonin