Expression profiling and electrophysiological studies suggest a major role for Orai1 in the store-operated Ca2+ influx pathway of platelets and megakaryocytes.
Store-operated Ca2+ influx represents a major route by which cytosolic Ca2+ can be elevated during platelet activation, yet its molecular identity in this cell type remains highly controversial. Using quantitative RT-PCR analysis of candidate receptor-operated cation entry pathways in human platelets, we show a >30-fold higher expression of message for the recently discovered Orai1 store-operated Ca2+ channel, and also the store Ca2+ sensor STIM1, when compared to the non-selective cation channels TRPC1, TRPC6 and TRPM2. Orai1 and STIM1 gene transcripts were also detected at higher levels than TRPC1, TRPC6 and TRPM2 in primary murine megakaryocytes and human megakaryocytic cell lines. In direct electrophysiological recordings from murine megakaryocytes, Ca2+ ionophore-induced store depletion stimulated CRAC currents, which are known to require Orai1, and these overlapped with TRPC6-like currents following P2Y receptor activation. Together with recent transgenic studies, these data provide evidence for STIM1:Orai1 as a primary pathway for agonist-evoked Ca2+ influx in the platelet and megakaryocyte.
Tolhurst
Gwen
G
Department of Physiology, Development & Neuroscience, University of Cambridge, Cambridge CB23EG, UK.
Carter
Richard N
RN
Amisten
Stefan
S
Holdich
Jon P
JP
Erlinge
David
D
Mahaut-Smith
Martyn P
MP
D000818:Animals; D001792:Blood Platelets / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000235:genetics / Q000502:physiology*; D002460:Cell Line; D004594:Electrophysiology; D020869:Gene Expression Profiling; D006801:Humans; D008533:Megakaryocytes / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics; D051379:Mice; D009363:Neoplasm Proteins / Q000235:genetics; D000071740:ORAI1 Protein; D012333:RNA, Messenger / Q000032:analysis; D000071737:Stromal Interaction Molecule 1
D015220:Calcium Channels; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D000071740:ORAI1 Protein; C510746:ORAI1 protein, human; D012333:RNA, Messenger; C103530:STIM1 protein, human; D000071737:Stromal Interaction Molecule 1; D002118:Calcium