Abstract Platelet exocytosis is regulated partially by the granular/cellular membrane lipids and proteins. Some platelets contain a membrane-bound tube, called an open canalicular system (OCS), which assists in granular release events and increases the membrane surface area for greater spreading. The OCS is not found in all species, and variations in membrane composition can cause changes in platelet secretion. Since platelet studies use various animal models, it is important to understand how platelets differ in both their composition and granular release to draw conclusions among various models. The relative phospholipid composition of the platelets with (mouse, rabbit) and without (cow) an OCS was quantified using UPLC-MS/MS. Cholesterol and protein composition was measured using an Amplex Red Assay and BCA Assay. TEM and dark field platelet images were gathered and analyzed with Image J. Granular release was monitored with single cell carbon fiber microelectrode amperometry. Cow platelets contained greater amounts of cholesterol and sphingomyelin. In addition, they yield greater serotonin release and longer δ granule secretion times. Finally, they showed greater spreading area with a greater range of spread. Platelets containing an OCS had more similarities in their membrane composition and secretion kinetics compared to cow platelets. However, cow platelets showed greater fusion pore stability which could be due to extra sphingomyelin and cholesterol, the primary components of lipid rafts. In addition, their greater stability may lead to many granules assisting in spreading. This study highlights fundamental membrane differences and their effects on platelet secretion.
Bibliographical noteFunding Information:
This work was supported by a Searle Foundation Fellowship and NIH New Innovator Award to CLH and NIGMS Biotechnology Training Program Fellowship ( 5T32GM008347-23 ) to SMG. The authors would like to thank Allison Mayenschein for assisting in the rabbit blood draw as well as Christa Marten and Nathaniel McDonald from the University of Minnesota Dairy Department for cow blood draws. We also would like to thank Emily Woo and Dr. Shencheng Ge for allowing us to measure features in their rabbit platelet TEM images and Dr. Joseph J. Dalluge for help with the mass spectrometry method development.
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- Open canalicular system