title: Sustained diacylglycerol formation from inositol phospholipids in angiotensin II-stimulated vascular smooth muscle cells.
abstract: Angiotensin II acts on cultured rat aortic vascular smooth muscle cells to stimulate phospholipase C-mediated hydrolysis of membrane phosphoinositides and subsequent formation of diacylglycerol and inositol phosphates. In intact cells, angiotensin II induces a dose-dependent increase in diglyceride which is detectable after 5 s and sustained for at least 20 min. Angiotensin II (100 nM)-stimulated diglyceride formation is biphasic, peaking at 15 s (227 +/- 19% control) and at 5 min (303 +/- 23% control). Simultaneous analysis of labeled inositol phospholipids shows that at 15 s phosphatidylinositol 4,5-bisphosphate (PIP2) and phosphatidylinositol 4-phosphate (PIP) decline to 52 +/- 6% control and 63 +/- 5% control, respectively, while phosphatidylinositol (PI) remains unchanged. In contrast, at 5 min, PIP2 and PIP have returned toward control levels (92 +/- 2 and 82 +/- 4% control, respectively), while PI has decreased substantially (81 +/- 2% control). The calcium ionophore ionomycin (15 microM) stimulates diglyceride accumulation but does not cause PI hydrolysis. 4 beta-Phorbol 12-myristate 13-acetate, an activator of protein kinase C, inhibits early PIP and PIP2 breakdown and diglyceride formation, without inhibiting late-phase diglyceride accumulation. Thus, angiotensin II induces rapid transient breakdown of PIP and PIP2 and delayed hydrolysis of PI. The rapid attenuation of polyphosphoinositide breakdown is likely caused by a protein kinase C-mediated inhibition of PIP and PIP2 hydrolysis. While in vascular smooth muscle stimulated with angiotensin II inositol 1,4,5-trisphosphate formation is transient, diglyceride production is biphasic, suggesting that initial and sustained diglyceride formation from the phosphoinositides results from different biochemical and/or cellular processes.
mesh_terms: D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects / Q000378:metabolism; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000378:metabolism; D002478:Cells, Cultured; D004075:Diglycerides / Q000096:biosynthesis*; D005989:Glycerides / Q000096:biosynthesis*; D007700:Kinetics; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D010716:Phosphatidylinositols / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism; D051381:Rats; D014316:Tritium
chemical_list: D001095:Arachidonic Acids; D004075:Diglycerides; D005989:Glycerides; D010716:Phosphatidylinositols; D010743:Phospholipids; D014316:Tritium; D000804:Angiotensin II; D016718:Arachidonic Acid