title: Kinetics of a cellular nitric oxide/cGMP/phosphodiesterase-5 pathway.
abstract: Rat platelets served as a model to evaluate quantitatively how guanylate cyclase (GC)-coupled nitric oxide (NO) receptors and phosphodiesterases (here phosphodiesterase-5) interact to transduce NO signals in cells. The platelets expressed mRNA only for the alpha(1) and beta(1) GC-coupled receptor subunits. In intact platelets, the potency of NO for elevating cGMP (EC(50) = 10 nm) was lower than in lysed platelets (EC(50) = 1.7 nm). The limiting activities of GC and phosphodiesterase in intact platelets were both very high, being equivalent to about 100 microm/s. With low phosphodiesterase activity (imposed by 100 microm sildenafil), the cGMP response over time was hyperbolic in shape for a range of NO concentrations or GC activities due to GC desensitization. Without a phosphodiesterase inhibitor, NO generated only brief cGMP transients, peaking after 2-5 s but amounting maximally to about 150 microm cGMP. The transients were caused partly by GC desensitization, which varied in rate (half-time up to 3 s) and extent (up to 80%) depending on the NO concentration, and partly by an enhancement of the phosphodiesterase catalytic activity with time, which was deduced to be up to 30-fold and to occur with a half-time of up to 5 s. The results were simulated by a quantitative model, which also explains the varied shapes of cGMP responses to NO found in other cells. Downstream phosphorylation in platelets was detectable within 2 s, and, with continuous exposure (1 min), this pathway could be engaged by subnanomolar NO concentrations (EC(50) = 0.5 nm).
authors.affiliation: Wolfson Institute for Biomedical Research, University College London, Gower Street, London WC1E 6BT, United Kingdom.
authors.forename: Elaine
authors.initials: E
authors.lastname: Mo
authors.forename: Hemisha
authors.initials: H
authors.lastname: Amin
authors.forename: Isaac H
authors.initials: IH
authors.lastname: Bianco
authors.forename: John
authors.initials: J
authors.lastname: Garthwaite
mesh_terms: D015106:3',5'-Cyclic-GMP Phosphodiesterases; D000818:Animals; D001792:Blood Platelets / Q000378:metabolism; D006152:Cyclic GMP / Q000378:metabolism*; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5; D017931:DNA Primers / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D007700:Kinetics; D009569:Nitric Oxide / Q000378:metabolism*; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism*; D010766:Phosphorylation; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D013997:Time Factors
chemical_list: D017931:DNA Primers; D012333:RNA, Messenger; D009569:Nitric Oxide; D010727:Phosphoric Diester Hydrolases; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5; C517384:Pde5a protein, rat; D006152:Cyclic GMP