title: Evidence that additional mechanisms to cyclic GMP mediate the decrease in intracellular calcium and relaxation of rabbit aortic smooth muscle to nitric oxide.
abstract: 1. The role of cyclic GMP in the ability of nitric oxide (NO) to decrease intracellular free calcium concentration [Ca2+]i and divalent cation influx was studied in rabbit aortic smooth muscle cells in primary culture. In cells stimulated with angiotensin II (AII, 10(-1) M), NO (10(-10) - 10(-6) M) increased cyclic GMP levels measured by radioimmunoassay and decreased [Ca2+]i and cation influx as indicated by fura-2 fluorimetry. 2. Zaprinast (10(-4) M), increased NO-stimulated levels of cyclic GMP by 3-20 fold. Although the phosphodiesterase inhibitor lowered the level of [Ca2+]i reached after administration of NO, the initial decreases in [Ca2+]i initiated by NO were not significantly different in magnitude or duration from those that occurred in the absence of zaprinast. 3. The guanylyl cyclase inhibitor, H-(1,2,4) oxadiazolo(4,3-a) quinoxallin-1-one (ODQ, 10(-5) M), blocked cyclic GMP accumulation and activation of protein kinase G, as measured by back phosphorylation of the inositol trisphosphate receptor. ODQ and Rp-8-Br-cyclic GMPS, a protein kinase G inhibitor, decreased the effects of NO, 10(-10) - 10(-8) M, but the decrease in [Ca2+]i or cation influx caused by higher concentrations of NO (10(-7) - 10(-6) M) were unaffected. Relaxation of intact rabbit aorta rings to NO (10(-7) - 10(-5) M) also persisted in the presence of ODQ without a significant increase in cyclic GMP. Rp-8-Br-cyclic GMPS blocked the decreases in cation influx caused by a cell permeable cyclic GMP analog, but ODQ and/or the protein kinase G inhibitor had no significant effect on the decrease caused by NO. 4. Although inhibitors of cyclic GMP, protein kinase G and phosphodiesterase can be shown to affect the decrease in [Ca2+]i and cation influx via protein kinase G, these studies indicate that when these mechanisms are blocked, cyclic GMP-independent mechanisms also contribute significantly to the decrease in [Ca2+]i and smooth muscle relaxation to NO.
authors.affiliation: Evans Department of Clinical Research, Whitaker Cardiovascular Institute, Boston University Medical Center, Massachusetts, USA.
authors.forename: R M
authors.initials: RM
authors.lastname: Weisbrod
authors.forename: M C
authors.initials: MC
authors.lastname: Griswold
authors.forename: M
authors.initials: M
authors.lastname: Yaghoubi
authors.forename: P
authors.initials: P
authors.lastname: Komalavilas
authors.forename: T M
authors.initials: TM
authors.lastname: Lincoln
authors.forename: R A
authors.initials: RA
authors.lastname: Cohen
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D015106:3',5'-Cyclic-GMP Phosphodiesterases / Q000037:antagonists & inhibitors; D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D001011:Aorta / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D002118:Calcium / Q000378:metabolism*; D006152:Cyclic GMP / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006162:Guanylate Cyclase / Q000037:antagonists & inhibitors; D008345:Manganese / Q000378:metabolism; D009126:Muscle Relaxation / Q000187:drug effects*; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D009569:Nitric Oxide / Q000494:pharmacology*; D010069:Oxadiazoles / Q000494:pharmacology; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D011688:Purinones / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D011817:Rabbits; D013873:Thionucleotides / Q000494:pharmacology; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology*
chemical_list: C095284:1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one; D004791:Enzyme Inhibitors; D010069:Oxadiazoles; D010726:Phosphodiesterase Inhibitors; D011688:Purinones; D011810:Quinoxalines; D013873:Thionucleotides; D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; D000804:Angiotensin II; C083763:8-bromoguanosino-3',5'-cyclic monophosphorothioate; D009569:Nitric Oxide; D008345:Manganese; D011493:Protein Kinase C; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D006162:Guanylate Cyclase; C011145:zaprinast; D006152:Cyclic GMP; D002118:Calcium; D015056:1-Methyl-3-isobutylxanthine