Effects of small latex particle uptake on the surface connected canalicular system of blood platelets: a freeze-fracture and cytochemical study.

Recent investigations have suggested that channels of the surface connected open canalicular system are the major source of membrane contributing to increased surface area of platelets following activation or uptake of particulates. However, study of large latex particle phagocytosis suggested that channels filled with spherules become dilated and lose connections with the outer surface, but do not become extruded onto the platelet membrane. The present study has employed electron dense tracers, freeze-fracture and transmission electron microscopy to follow the uptake of small latex spherules by blood platelets. Small particles were rapidly incorporated into the numerous channels without causing significant changes in surface or internal morphology. Intramembranous particles on both E and P faces in replicas of freeze-fractured platelets were unaffected by ingestion of latex spherules. Prolonged exposure to small latex particles caused platelets to lose their discoid form. The irregular spheres contained two or three dilated vacuoles filled with latex and a reduced number of single channels. Results of this and previous studies suggest that channels of the open canalicular system are internalized in platelets after phagocytosis, and are not extruded onto the platelet surface.