Thromb Haemost 2020; 120(07): 1075-1086
DOI: 10.1055/s-0040-1712447
Cellular Haemostasis and Platelets
Georg Thieme Verlag KG Stuttgart · New York

Function of Large and Small Platelets Differs, Depending on Extracellular Calcium Availability and Type of Inductor

Stefan Handtke
1  Institut für Immunologie und Transfusionsmedizin, Abteilung Transfusionsmedizin, Universitätsmedizin Greifswald, Greifswald, Germany
,
Jan Wesche
1  Institut für Immunologie und Transfusionsmedizin, Abteilung Transfusionsmedizin, Universitätsmedizin Greifswald, Greifswald, Germany
,
1  Institut für Immunologie und Transfusionsmedizin, Abteilung Transfusionsmedizin, Universitätsmedizin Greifswald, Greifswald, Germany
,
Andreas Greinacher
1  Institut für Immunologie und Transfusionsmedizin, Abteilung Transfusionsmedizin, Universitätsmedizin Greifswald, Greifswald, Germany
,
Thomas Thiele
1  Institut für Immunologie und Transfusionsmedizin, Abteilung Transfusionsmedizin, Universitätsmedizin Greifswald, Greifswald, Germany
› Author Affiliations
Funding The study was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Projektnummer 374031971–TRR 240.
Further Information

Publication History

02 December 2019

18 April 2020

Publication Date:
11 June 2020 (online)

Abstract

It is widely anticipated that large platelets are more reactive than small platelets. This was mainly shown in Ca2+-poor media albeit extracellular Ca2+ is utilized by platelets for activation. We determined the impact of extracellular Ca2+ on functional differences between large and small platelets in response to thrombin receptor activating peptide 6 (TRAP-6), adenosine diphosphate (ADP), and epinephrine. In Ca2+-poor buffer, large platelets responded stronger to TRAP-6 which equalized in Ca2+ containing buffer. Large platelets contained and mobilized more Ca2+ from their intracellular stores upon TRAP-6 stimulation explaining their better reactivity in Ca2+-poor media. Stronger aggregation of large platelets in response to ADP also equalized in presence of Ca2+, whereas large platelets responded weaker to ADP in flow cytometry (CD62P-expression: 9.7 mean fluorescence intensity [MFI] [4.4–17.9] vs. 17.5 MFI [6.1–45.6], p = 0.0234) and PAC-1 binding (11.1 MFI [5.7–19.6] vs. 20.5 MFI [14.4–35.0], p = 0.0078). Epinephrine response was stronger in large platelets (CD62P-expression: 11.8 MFI [6.8–33.0] vs. 6.8 MFI [2.5–15.2], p = 0.0078; PAC-1 binding 18.9 MFI [13.6–38.4] vs. 13.0 MFI [6.8–22.4], p = 0.0234; max. aggregation 82.9% [58.7–94.8] vs. 77.2% [19.8–88.8], p = 0.0313), which expressed more α2A receptors. Epinephrine further increased phosphatidylserine (PS) exposure especially in large platelets. PS-positive platelets progressively divided into two subpopulations with high or basic intracellular Ca2+ dependent on extracellular Ca2+. Thrombin generation was faster with small, but accelerated by PS exposure and epinephrine-coactivated large platelets. We show that responses of large and small platelets differ depending on extracellular Ca2+ availability and the inductor. Careful control of extracellular Ca2+ is necessary in functional studies with large and small platelets.

Authors' Contributions

S.H. and T.T. designed the experiments; S.H., J.W., and R.P. performed the experiments; S.H., A.G., and T.T. analyzed the data; S.H., A.G., and T.T. wrote the manuscript. All authors contributed to manuscript revision, read and approved the submitted version.


Supplementary Material