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Platelets from Munc18c heterozygous mice exhibit normal stimulus-induced release

Journal: Thrombosis and Haemostasis
ISSN: 0340-6245
Topic:

Paediatric Haemostasis

DOI: http://dx.doi.org/10.1160/TH04-04-0263
Issue: 2004: 92/4 (Oct) pp. 672-895
Pages: 829-837

Platelets from Munc18c heterozygous mice exhibit normal stimulus-induced release

Todd D. Schraw1, Garland L. Crawford1, Qiansheng Ren1,Wangsun Choi1, Debbie C.Thurmond2, Jeffery Pessin3, Sidney W. Whiteheart1
1Department of Molecular and Cellular Biochemistry, University of Kentucky College of Medicine, Lexington, Kentucky, USA 2Department of Biochemistry and Molecular Biology, Center for Diabetes Research, Indiana University School of Medicine, Indianapolis

Summary

A critical aspect of hemostasis is the release of clot-forming components from the three intra-platelet stores: dense core granules, a-granules and lysosomes. Exocytosis from these granules is mediated by soluble (SNAPs and NSF) and integralmembrane proteins (v- and t-SNAREs).Three SM (Sec1/Munc18) proteins are present in mouse platelets (Munc18a, 18b and 18c) and each potentially regulates exocytosis via modulation of their cognate syntaxin binding partner.To define the molecular machinery required for platelet exocytosis, we analyzed platelets from Munc18c heterozygous knockout mice.These platelets show a decrease in Munc18c but no apparent reduction in other secretory machinery components. No differences in the rates of aggregation or of secretion of [3H]-5HT (dense core granules), platelet factor 4 (a-granules), or hexosaminidase (lysosomes) were detected between platelets from Munc18c heterozygous knockout or wild-type mice. The platelets also show normal morphology. Contrary to a predicted requirement for Munc18c in platelet secretion, data reported here show that reducing Munc18c levels does not substantially alter platelet function.These data show that despite Munc18c’s role in platelet secretion, the lack of a secretion defect may be attributed to compensation by other Munc18 isoforms or that one allele is sufficient to maintain secretion under standard conditions.