Evidence of Selective Packaging and Different α-Granule Subtypes in Canine Platelets

Platelets are circulating megakaryocytic cytoplasmic fragments that are required to maintain vascular integrity and prevent haemorrhage. During activation, platelets release hundreds of bioactive proteins, mainly by secretion of α-granule content. These proteins include von Willebrand factor (vWF) and fibrinogen, major adhesive proteins involved in haemostasis. Human and mouse platelet α-granules are packaged selectively to contain different molecules and platelets can differentially release these proteins on specific receptor activation. Confocal laser scanning microscopy was used to analyse vWF and fibrinogen localization within canine platelet α-granules. In resting canine platelets, the majority of platelet vWF and fibrinogen is located in separate α-granule populations. These findings provide evidence that canine platelets contain different α-granule subtypes, suggesting that selective protein packaging occurs during canine platelet ontology.