title: Defective diacylglycerol-induced Ca2+ entry but normal agonist-induced activation responses in TRPC6-deficient mouse platelets.
abstract: BACKGROUND
  Platelet adhesion, activation and aggregation at sites of vascular injury are essential processes for primary hemostasis. Elevation of the intracellular Ca(2+) concentration is a central event in platelet activation but the underlying mechanisms are not fully understood. Store-operated calcium entry (SOCE) through Orai1 was shown to be the main Ca(2+) influx pathway in murine platelets, but there are additional non-store-operated Ca(2+) (non-SOC) and receptor operated Ca(2+) (ROC) channels expressed in the platelet plasma membrane.
  
  
  OBJECTIVE
  Canonical transient receptor potential (TRPC) channel 6 is found both in human and murine platelets and has been proposed to mediate diacylglycerol (DAG) activated ROCE but also a role in the regulation of SOCE has been suggested.
  
  
  METHODS
  To investigate the function of TRPC6 in platelet Ca(2+) signaling and activation, we analyzed platelets from mice deficient in TRPC6 using a wide range of in vitro and in vivo assays.
  
  
  RESULTS
  In the mutant platelets, DAG activated Ca(2+) influx was found to be abolished. However, this did not significantly affect SOCE or agonist induced Ca(2+) responses. Platelet function in vitro and in vivo was also unaltered in the absence of TRPC6.
  
  
  CONCLUSIONS
  Our results indicate that DAG activated ROCE is mediated exclusively by TRPC6 in murine platelets, but this Ca(2+) influx has no major functional relevance for hemostasis and thrombosis. Further, in contrast to previous suggestions, based on studies with human platelets, TRPC6 appears to play an insignificant role in the regulation of SOCE in murine platelets.
authors.affiliation: Chair of Vascular Medicine, DFG Research Center for Experimental Biomedicine, University Hospital and Rudolf Virchow Center, University of Würzburg, Würzburg, Germany.
authors.forename: G
authors.initials: G
authors.lastname: Ramanathan
authors.forename: S
authors.initials: S
authors.lastname: Gupta
authors.forename: I
authors.initials: I
authors.lastname: Thielmann
authors.forename: I
authors.initials: I
authors.lastname: Pleines
authors.forename: D
authors.initials: D
authors.lastname: Varga-Szabo
authors.forename: F
authors.initials: F
authors.lastname: May
authors.forename: C
authors.initials: C
authors.lastname: Mannhalter
authors.forename: A
authors.initials: A
authors.lastname: Dietrich
authors.forename: B
authors.initials: B
authors.lastname: Nieswandt
authors.forename: A
authors.initials: A
authors.lastname: Braun
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000818:Animals; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D002097:C-Reactive Protein / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects; D002712:Chlorides; D004075:Diglycerides / Q000378:metabolism*; D004195:Disease Models, Animal; D005290:Ferric Compounds; D005786:Gene Expression Regulation; D008562:Membrane Glycoproteins / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D000071740:ORAI1 Protein; D015539:Platelet Activation; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D022142:Secretory Vesicles / Q000187:drug effects / Q000378:metabolism; D000071737:Stromal Interaction Molecule 1; D050052:TRPC Cation Channels / Q000172:deficiency* / Q000235:genetics; D000074287:TRPC6 Cation Channel; D013917:Thrombin / Q000378:metabolism; D013927:Thrombosis / Q000097:blood / Q000139:chemically induced / Q000235:genetics; D013997:Time Factors
chemical_list: D015220:Calcium Channels; D002712:Chlorides; D004075:Diglycerides; D005290:Ferric Compounds; D008562:Membrane Glycoproteins; D000071740:ORAI1 Protein; C520430:Orai1 protein, mouse; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D012333:RNA, Messenger; C100757:Stim1 protein, mouse; D000071737:Stromal Interaction Molecule 1; D050052:TRPC Cation Channels; D000074287:TRPC6 Cation Channel; C492146:Trpc6 protein, mouse; D000244:Adenosine Diphosphate; D002097:C-Reactive Protein; D013917:Thrombin; C024555:ferric chloride