Thromboxane A2-mediated shape change: independent of Gq-phospholipase C--Ca2+ pathway in rabbit platelets.

摘要: 1. Thromboxane A2 (TXA2) receptor-mediated signal transduction was investigated in washed rabbit platelets to clarify the mechanisms of induction shape change and aggregation. 2. The TXA2 agonist, U46619 (1 nM 10 microM) caused aggregation a concentration-dependent manner. A forty-times higher concentration needed for (EC50 0.58 than 0.013 microM). occurred only when external 1 mM Ca2+ present, but could occur absence Ca2+. 3. SQ29548 at 30 GR32191B 0.3 microM (TXA2 receptor antagonists) competitively inhibited U46619-induced with similar potency, showing that both induced by were events. However, ONO NT-126 nM, another antagonist, much more potently change, suggesting possible existence subtypes. 4. (2 3 itself without manner, independent Therefore, is partial agonist platelets. 5. (10 increased internal ([Ca2+]i) activated phosphoinositide (PI) hydrolysis manner concentration-dependency. 6. (3 also GTPase concentration-dependently membranes derived from activation partly treatment QL, an antibody against Gq/11. 7. EC50 values mobilization (0.15 microM), PI (0.20 increase activity (0.12 similar, different value (0.013 receptors might cause via unknown mechanism. 8. unaffected W-7 (30 calmodulin antagonist or ML-7 myosin light-chain kinase inhibitor, indicating [Ca2+]i not be involved change. In fact, nM) affecting level, determined simultaneous recordings. 9. [3H]-SQ29548 [3H]-U46619 bound single site Kd 14.88 Bmax 106.1 fmol/10(8) 129.8 170.4 platelets, respectively. inhibitory constant Ki as inhibitor 3H-ligand binding activity, mobilization, significantly (P < 0.001 Student's t test) effect on 10. Neither nor affected adenosine 3',5'-cyclic monophosphate (cyclic AMP) level presence and/or isobutyl methylxanthine. 11. results indicate stimulation causes phospholipase C G protein Gq/11 family leading Ca2+, involvement Gq-phospholipase C-Ca2+ pathway.