In situ observation of Dense-Body Release from Hydrated Human Platelets

Abstract

Dense bodies, electron-dense granules are believed to be storage sites for large pools of platelet serotonin, pyrophosphate, adenine nucleotides, and calcium. In order to prove that dense bodies exist as such in living platelets, we examined hydrated human platelets in the electron microscope, utilizing the differentially pumped hydration chamber.Human platelets were resuspended in the sodium chloride-Tris-citrate buffer with 0.35% bovine serum albumin, and were allowed to settle on carbon-coated grids covered with a thin film of liquid. Specimens were viewed and photographed at 100 kV in a Siemens 1A electron microscope equipped with an environmental chamber. The beam dose per micrograph was 5 x 10-5 coulombs/cm2. Although details of some platelets were obscured by a thick film of water, dense bodies were clearly visible in a large proportion of the platelets photographed (Figure 1). The distribution of platelets by dense-body content was similar to that described previously for air-dried whole mounts.