IP3 receptor blockade fails to prevent intracellular Ca2+ release by ET-1 and alpha-thrombin.
The effect of inositol 1,4,5-trisphosphate (IP3) receptor blockade on platelet-derived growth factor (PDGF), fibroblast growth factor (FGF), endothelin-1 (ET-1), or alpha-thrombin receptor-mediated intracellular Ca2+ (Ca2+i) release was examined using fura 2 microspectrofluorometry in single Chinese hamster ovary cells and myoblasts. Blockade of the IP3 receptor was achieved by microinjection of heparin or monoclonal antibody (MAb) 18A10 into the IP3 type 1 receptor. Heparin completely inhibited Ca2+i release after flash photolysis with caged IP3 and after exposure to PDGF and FGF. In contrast, heparin failed to block Ca2+i release after alpha-thrombin and ET-1. After application of ligand, IP3 levels were five- to sevenfold higher for alpha-thrombin than for ET-1 or PDGF. IP3 levels after PDGF and ET-1 were comparable. Similar to heparin, MAb 18A10 blocked Ca2+i release after PDGF but failed to block Ca2+i release after ET-1 or alpha-thrombin. These data suggest that the mechanisms of Ca2+i release by tyrosine kinase and certain 7-transmembrane receptors may differ. Although both receptor types use the IP3-signaling system, the ET-1 and alpha-thrombin receptors may have a second, alternative mechanism for activating CA2+i release.
Department of Pediatrics, University of California, San Francisco 94143, USA.
R S
RS
Mathias
K
K
Mikoshiba
T
T
Michikawa
A
A
Miyawaki
H E
HE
Ives
D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D016466:CHO Cells; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000276:immunology; D006224:Cricetinae; D019332:Endothelin-1 / Q000494:pharmacology*; D016222:Fibroblast Growth Factor 2 / Q000494:pharmacology; D005456:Fluorescent Dyes; D016257:Fura-2; D006493:Heparin / Q000494:pharmacology; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008845:Microinjections; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D051381:Rats; D044022:Receptor, Endothelin A; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry* / Q000276:immunology; D017466:Receptors, Endothelin / Q000235:genetics; D017468:Receptors, Fibroblast Growth Factor / Q000235:genetics; D017479:Receptors, Platelet-Derived Growth Factor / Q000235:genetics; D015290:Second Messenger Systems; D015398:Signal Transduction; D013917:Thrombin / Q000494:pharmacology*; D014162:Transfection
D000911:Antibodies, Monoclonal; D015220:Calcium Channels; D019332:Endothelin-1; D005456:Fluorescent Dyes; D053496:Inositol 1,4,5-Trisphosphate Receptors; D010982:Platelet-Derived Growth Factor; D044022:Receptor, Endothelin A; D018160:Receptors, Cytoplasmic and Nuclear; D017466:Receptors, Endothelin; D017468:Receptors, Fibroblast Growth Factor; D016222:Fibroblast Growth Factor 2; D006493:Heparin; D017479:Receptors, Platelet-Derived Growth Factor; D013917:Thrombin; D002118:Calcium; D016257:Fura-2