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Summary.  Background: Previous studies have shown platelet Ca2+ abnormalities in diabetes mellitus and some reports suggest abnormal platelet production. Platelet Ca2+ homeostasis is controlled by a multi‐Ca2+‐ATPase system that includes two plasma membrane Ca2+‐ATPase (PMCA) and seven sarco/endoplasmic reticulum Ca2+‐ATPase (SERCA) isoforms. In addition, we recently found that the expression of PMCA4b and SERCA3 isoforms may serve as new markers of abnormal megakaryocytopoiesis [Nurden P et al. Impaired megakaryocytopoiesis in type 2B von Willebrand disease with severe thrombocytopenia. Blood 2006; 108: 2587–95]. Aim: To analyze the expression of major platelet Ca2+‐ATPases in 27 patients with type 1 or type 2 diabetes (T1D or T2D) compared with normal donors. Methods: Investigation of protein and mRNA expressions of PMCA1b and PMCA4b, and SERCA2b, SERCA3a and SERCA3b, using specific Western blotting and reverse transcriptase‐polymerase chain reaction, respectively. Results: Remarkably, all patients with T1D were found to present a higher expression of PMCA4b protein (212% ± 28%; n = 10) and PMCA4b mRNA (155% ± 16%; n = 17), coupled with a higher expression of SERCA3b mRNA (165% ± 9%) in some cases. Patients with T2D (n = 10) were also studied for protein expression and were found to present similar major upregulation of the expression of PMCA4b protein (180% ± 28%; n = 10). Lastly, five of 10 patients with T1D were studied for PMCA4b expression after insulin treatment, with four of five recovering normal expression (96% ± 15%; n = 5). Conclusions: Compared with the expression of PMCA4b upon platelet maturation, platelets from diabetic patients exhibit similarities with immature megakaryocytes. Thus, this study reinforces the idea that abnormal megakaryocytopoiesis can provide additional insights into diabetes and could represent a novel therapeutic target for antithrombotic drugs.

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