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IP3 receptor blockade fails to prevent intracellular Ca2+ release by ET-1 and alpha-thrombin

R S Mathias1, K Mikoshiba, T Michikawa

  • 1Department of Pediatrics, University of California, San Francisco 94143, USA.

The American Journal of Physiology
|June 5, 1998
PubMed

Insights

Inositol 1,4,5-trisphosphate (IP3) receptor blockade differentially affects calcium release. While heparin and MAb 18A10 block PDGF and FGF, they do not inhibit ET-1 or alpha-thrombin signaling.

Area of Science:

  • Cellular signaling
  • Molecular biology
  • Calcium signaling pathways

Background:

  • Platelet-derived growth factor (PDGF), fibroblast growth factor (FGF), endothelin-1 (ET-1), and alpha-thrombin receptors mediate intracellular calcium (Ca2+i) release.
  • Inositol 1,4,5-trisphosphate (IP3) receptors are key mediators in calcium release.
  • Understanding differential signaling mechanisms is crucial for cell biology.

Purpose of the Study:

  • To investigate the role of IP3 receptor blockade in mediating Ca2+i release induced by various growth factors and agonists.
  • To elucidate potential differences in Ca2+i release mechanisms among different receptor types.

Main Methods:

  • Fura 2 microspectrofluorometry was employed in single Chinese hamster ovary cells and myoblasts.
  • IP3 receptor blockade was achieved via microinjection of heparin or monoclonal antibody (MAb) 18A10.
  • Cells were stimulated with caged IP3, PDGF, FGF, ET-1, or alpha-thrombin to assess Ca2+i release.

Main Results:

  • Heparin completely inhibited Ca2+i release induced by caged IP3, PDGF, and FGF, but not by alpha-thrombin or ET-1.
  • MAb 18A10 blocked Ca2+i release stimulated by PDGF but not by ET-1 or alpha-thrombin.
  • IP3 levels were significantly higher for alpha-thrombin stimulation compared to ET-1 or PDGF.

Conclusions:

  • Tyrosine kinase receptors (PDGF, FGF) and certain 7-transmembrane receptors (ET-1, alpha-thrombin) utilize distinct Ca2+i release mechanisms.
  • While both receptor types engage the IP3 signaling system, ET-1 and alpha-thrombin receptors may possess alternative pathways for Ca2+i release activation.

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