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Thrombosis research

Altered platelet calsequestrin abundance, Na⁺/Ca²⁺ exchange and Ca²⁺ signaling responses with the progression of diabetes mellitus.


PMID 25084748

Abstract

Downregulation of calsequestrin (CSQ), a major Ca(2+) storage protein, may contribute significantly to the hyperactivity of internal Ca(2+) ([Ca(2+)]i) in diabetic platelets. Here, we investigated changes in CSQ-1 abundance, Ca(2+) signaling and aggregation responses to stimulation with the progression of diabetes, especially the mechanism(s) underlying the exaggerated Ca(2+) influx in diabetic platelets. Type 1 diabetes was induced by streptozotocin in rats. Platelet [Ca(2+)]i and aggregation responses upon ADP stimulation were assessed by fluorescence spectrophotometry and aggregometry, respectively. CSQ-1 expression was evaluated using western blotting. During the 12-week course of diabetes, the abundance of CSQ-1, basal [Ca(2+)]i and ADP-induced Ca(2+) release were progressively altered in diabetic platelets, while the elevated Ca(2+) influx and platelet aggregation were not correlated with diabetes development. 2-Aminoethoxydiphenyl borate, the store-operated Ca(2+) channel blocker, almost completely abolished ADP-induced Ca(2+) influx in normal and diabetic platelets, whereas nifedipine, an inhibitor of the nicotinic acid adenine dinucleotide phosphate receptor, showed no effect. Additionally, inhibition of Na(+)/Ca(2+) exchange induced much slower Ca(2+) extrusion and more Ca(2+) influx in normal platelets than in diabetic platelets. Furthermore, under the condition of Ca(2+)-ATPase inhibition, ionomycin caused greater Ca(2+) mobilization and Ca(2+) influx in diabetic platelets than in normal platelets. These data demonstrate that platelet hyperactivity in diabetes is caused by several integrated factors. Besides the downregulation of CSQ-1 that mainly disrupts basal Ca(2+) homeostasis, insufficient Na(+)/Ca(2+) exchange also contributes, at least in part, to the hyperactive Ca(2+) response to stimulation in diabetic platelets.