Summary
Platelets from seven normal subjects were fractionated on continuous Percoll density
gradients and low density (LD), intermediate, and high density (HD) platelets were
prepared for transmission electron microscopy followed by computerised morphometric
analysis. Normal ultrastructural appearance and discoid shape were preserved by incubation
of the platelets in nutrient medium at 37 °C immediately before fixation. HD platelet
sections had a larger mean cross-sectional area but a lower ratio of the major to
the minor axis compared to LD platelet sections. HD platelets contained more alpha
granules, dense granules and mitochondria per square micron of section area than LD
platelets. The percentage of section area occupied by open canalicular system was
greater in the LD platelets while the percentage area occupied by glycogen fields
was over ten-fold higher in the HD platelets. The mean cross-sectional areas of individual
alpha granules and dense granules increased with density while the opposite trend
was found for mitochondria. It is suggested that these ultrastructural differences
mainly arise during thrombopoiesis and may indicate some functional specialization
among platelets.
Key words
Platelet density - Platelet ultrastructure - Morphometric analysis
