Thromboxane A2 stimulated signal transduction in vascular smooth muscle.
Thromboxane A2 (TXA2) is a potent, labile vasoconstrictor which stimulates vessel contraction through vascular smooth muscle TXA2 receptors differing from those in platelets. We studied TXA2-stimulated events in cultured adult rat aortic smooth muscle cells. The stable TXA2 mimetic (15S)-hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5Z, 13E-dienoic acid (U46619) competed for TXA2 agonist binding to vascular smooth muscle cells with an IC50 of 10 +/- 1 nM. In fura-2-loaded cells, U46619 increased free cytosolic Ca++ concentration with an EC50 of 49 +/- 14 nM. The increase in free cytosolic Ca++ was rapid, transient and independent of extracellular Ca++ or Ca++ antagonists and thus was due to release from intracellular stores. U46619-mediated Ca++ release was temporally associated with phosphorylation of myosin light chains, increased accumulation of 1,4,5-inositol trisphosphate (EC50 = 32 +/- 4 nM) and cytoplasmic acidification from pH 7.06 +/- 0.01 to 7.00 +/- 0.02 (P = .02). Ca++ release was 53% attenuated by the phospholipase C inhibitor, 1-[6-[[17 beta-3-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H- pyrrole-2,5-dione. In rat aortic rings U46619 caused TXA2 receptor-mediated contractions (EC50 of 28 +/- 2 nM) which were not attenuated by removal of extracellular Ca++ from the superfusion buffer. Together, these results suggest that agonist occupation of TXA2 receptors produces vascular smooth muscle contraction through initial activation of phospholipase C with production of 1,4,5-inositol phosphate, release of intracellular calcium stores and phosphorylation of myosin light chains associated with cellular acidification, presumably via activation of Ca++ ATPase.
Dorn
G W
GW
Department of Medicine/Cardiology, University of Cincinnati College of Medicine, Ohio.
Becker
M W
MW
D000818:Animals; D002478:Cells, Cultured; D006863:Hydrogen-Ion Concentration; D007295:Inositol Phosphates / Q000378:metabolism; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism; D009219:Myosin-Light-Chain Kinase / Q000378:metabolism; D010766:Phosphorylation; D011450:Prostaglandin Endoperoxides, Synthetic / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D017482:Receptors, Thromboxane / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects*; D013928:Thromboxane A2 / Q000494:pharmacology*
D007295:Inositol Phosphates; D011450:Prostaglandin Endoperoxides, Synthetic; D017482:Receptors, Thromboxane; D013928:Thromboxane A2; D009219:Myosin-Light-Chain Kinase