title: Altered platelet calsequestrin abundance, Na⁺/Ca²⁺ exchange and Ca²⁺ signaling responses with the progression of diabetes mellitus.
abstract: BACKGROUND
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Pharmacology, Capital Medical University, Beijing 100069, P.R. China; Beijing Key Laboratory of Metabolic Disorders Related Cardiovascular Diseases, Beijing 100069, P.R. China.
authors.forename: Yuanyuan
authors.initials: Y
authors.lastname: Zheng
authors.affiliation: Department of Pharmacology, Capital Medical University, Beijing 100069, P.R. China; Beijing Key Laboratory of Metabolic Disorders Related Cardiovascular Diseases, Beijing 100069, P.R. China.
authors.forename: Limin
authors.initials: L
authors.lastname: Wang
authors.affiliation: Department of Pharmacology, Capital Medical University, Beijing 100069, P.R. China; Beijing Key Laboratory of Metabolic Disorders Related Cardiovascular Diseases, Beijing 100069, P.R. China.
authors.forename: Zhixiang
authors.initials: Z
authors.lastname: Zhu
authors.affiliation: Department of Pharmacology, Capital Medical University, Beijing 100069, P.R. China; Beijing Key Laboratory of Metabolic Disorders Related Cardiovascular Diseases, Beijing 100069, P.R. China.
authors.forename: Xinxin
authors.initials: X
authors.lastname: Yan
authors.affiliation: Department of Pharmacology, Capital Medical University, Beijing 100069, P.R. China; Beijing Key Laboratory of Metabolic Disorders Related Cardiovascular Diseases, Beijing 100069, P.R. China.
authors.forename: Lane
authors.initials: L
authors.lastname: Zhang
authors.affiliation: Department of Pharmacology, Capital Medical University, Beijing 100069, P.R. China; Beijing Key Laboratory of Metabolic Disorders Related Cardiovascular Diseases, Beijing 100069, P.R. China.
authors.forename: Pingxiang
authors.initials: P
authors.lastname: Xu
authors.affiliation: Department of Pharmacology, Capital Medical University, Beijing 100069, P.R. China; Beijing Key Laboratory of Metabolic Disorders Related Cardiovascular Diseases, Beijing 100069, P.R. China. Electronic address: luodl@ccmu.edu.cn.
authors.forename: Dali
authors.initials: D
authors.lastname: Luo
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000818:Animals; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects; D002135:Calcium-Binding Proteins / Q000097:blood*; D002155:Calsequestrin; D003921:Diabetes Mellitus, Experimental / Q000097:blood* / Q000139:chemically induced; D003922:Diabetes Mellitus, Type 1 / Q000097:blood* / Q000139:chemically induced; D018450:Disease Progression; D015536:Down-Regulation; D008297:Male; D010974:Platelet Aggregation; D017207:Rats, Sprague-Dawley; D019831:Sodium-Calcium Exchanger / Q000097:blood*; D013311:Streptozocin; D013997:Time Factors
chemical_list: D002135:Calcium-Binding Proteins; D002155:Calsequestrin; D019831:Sodium-Calcium Exchanger; C057137:Casq1 protein, rat; D013311:Streptozocin; D000244:Adenosine Diphosphate
keywords: Ca(2+) signaling; Calsequestrin-1; Diabetes; Na(+)/Ca(2+) exchange; Platelet aggregation