Modulators of intraplatelet calcium concentration affect the binding of thrombospondin to blood platelets in healthy donors and patients with type 2 diabetes mellitus.
Thrombospondin (TSP), which is secreted from alpha-granules of activated platelets, binds to its surface receptor (CD36) in the presence of Ca2+.


OBJECTIVE
We monitored how the modulation of intraplatelet Ca2+ affects TSP binding to CD36 on platelets from healthy donors and patients with type 2 diabetes mellitus. We also aimed to verify whether the impaired Ca2+ mobilisation in diabetes influences TSP binding upon the pharmacological modulation of calcium transport.


METHODS
Whole blood cytometry was used to monitor TSP release/binding and CD36 presentation in platelets from 28 type 2 patients and 33 healthy donors.


RESULTS
No significant changes in TSP and CD36 levels were revealed between the groups in circulating platelets and TRAP-, collagen- or thrombin-activated platelets. In healthy donors, 1 microM thapsigargin (TG) elevated the TRAP-activated TSP binding (by up to 50%, p<0.001), 5 mM EGTA reversed the effect (by up to 85%, p<0.001), and overcame the effect of TG when used together. Less profoundly expressed effects occurred in the NIDDM group. In both groups TG increased the presentation of CD36 in TRAP-stimulated platelets (p<0.05), whereas EGTA lowered the TRAP-stimulated increase in CD36 (p<0.001). The inhibition of CD36 by EGTA was stronger in healthy volunteers (41% vs. 32%, respectively, p<0.05), whereas the activation by TG was higher in the NIDDM group (11% vs. 27%, p<0.05). When acting together the suppressive effects of EGTA on TG-dependent Ca2+ mobilisation were much attenuated in diabetic subjects (p<0.05).


CONCLUSIONS
Both the release of TSP and CD36 presentation are under the influence of agents modulating intracellular Ca2+. Diabetic platelets seem more vulnerable to the releasers of cytosolic [Ca2+] and more resistant to the blockers of cytosolic [Ca2+] mobilisation.
Wieclawska
B
B
Laboratory of Haemostasis and Haemostatic Disorders, Medical University of Lodz, Lodz, Poland.
Rozalski
M
M
Trojanowski
Z
Z
Watala
C
C
D000328:Adult; D000368:Aged; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D018955:CD36 Antigens / Q000187:drug effects / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D003924:Diabetes Mellitus, Type 2 / Q000097:blood*; D005260:Female; D006801:Humans; D008297:Male; D016555:Matched-Pair Analysis; D008875:Middle Aged; D019007:P-Selectin / Q000378:metabolism; D015539:Platelet Activation / Q000187:drug effects; D011485:Protein Binding; D019699:Thrombospondins / Q000187:drug effects / Q000378:metabolism*
D018955:CD36 Antigens; D019007:P-Selectin; D019699:Thrombospondins; D002118:Calcium