Ca2+ spike initiation from sensitized inositol 1,4,5-trisphosphate-sensitive Ca2+ stores in megakaryocytes

Masahiro Ikeda, Kiyoshi Kurokawa, Yoshio Maruyama

Research output: Contribution to journalArticlepeer-review

5 Citations (Scopus)


Ca2+-mediated Ca2+ spikes were analysed in fura-2-loaded megakaryocytes. Direct Ca2+ loading using whole-cell dialysis induced an all-or-none Ca2+ spike on top of a tonic increase in cellular Ca2+ concentration ([Ca2+]i) with a latency of 3-7 s. The latency decreased with increasingly higher concentrations of Ca2+ in the dialysing solution. Spike size and its initiation did not correlate with the tonic level of [Ca2+]i. Thapsigargin completely abolished the Ca2+-induced spike initiation, suggesting that Ca2+ spikes originate from thapsigargin-sensitive Ca2+ pools. An inhibitor of phosphatidylinositide-specific phospholipase C (PLC), 2-nitro-4-carboxyphenyl-N,N-diphenyl-carbamate prolonged the latency without changes of spike size in most cases (6/9 cells), but abolished the spike initiation in the other cells (3/9). The results suggest that an increase in [Ca2+]i charges up the inositol-1,4,5-trisphosphate(Ins P3)- and thapsigargin-sensitive Ca2+ pools which progressively sensitize to low or slightly elevated levels of InsP3 by the action of Ca2+-dependent PLC until a critical Ca2+ content is reached, and then the Ca2+ spike is triggered. Thus, the limiting step of Ca2+ spike triggering is the initial filling process and the level of InsP3 in megakaryocytes.

Original languageEnglish
Pages (from-to)355-364
Number of pages10
JournalPflügers Archiv European Journal of Physiology
Issue number3-4
Publication statusPublished - 1994 Jun 1


  • Calcium spikes
  • Inositol 1,4,5-trisphosphate
  • Internal calcium
  • Megakaryocyte
  • Sensitization

ASJC Scopus subject areas

  • Physiology
  • Clinical Biochemistry
  • Physiology (medical)


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