Role of high affinity cAMP phosphodiesterase activities in the response of S49 cells to agonists.
Quantitative analysis of a drug or hormone action expressed through increased rates of cAMP synthesis is dependent on the activities and affinities of the phosphodiesterases (PDEs) that hydrolyze the cAMP. It is shown herein that, on both theoretical and experimental grounds, significant contribution to hydrolysis by high affinity PDE activity would lead to striking departures from proportionality of the relationships between rates of cAMP synthesis and intracellular cAMP accumulations. Simulations of cAMP decay curves, cellular concentration-response curves to agonists, and cAMP time courses were used to predict the consequences of a high affinity PDE in an intact cell experimental system. Specifically, the simulations predicted 1) an upward convexity in the cAMP log-decay curve, 2) an upward concavity in the concentration-response curve, and 3) the amplification of small differences in initial rates resulting in large differences in accumulation at long times. S49 WT lymphoma cells demonstrated properties that fitted the predictions of the simulations in an experimental system. We conclude that the presence of significant high affinity PDEs has a profound effect on the nature of the response of cells to agonists and antagonists of the adenylate cyclase system. In addition, intracellular rates of hydrolysis were compared with PDE activities measured in cell-free systems. The data showed that cell-free estimates of PDE activity seriously overestimated the intracellular rates of cAMP hydrolysis.
Barber
R
R
Laboratories of Cyclic Nucleotide Research, Graduate School of Biomedical Sciences, University of Texas Health Science Center, Houston 77030.
Goka
T J
TJ
Butcher
R W
RW
D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000032:analysis / Q000502:physiology*; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004837:Epinephrine / Q000494:pharmacology; D006868:Hydrolysis; D007700:Kinetics; D013997:Time Factors
D000242:Cyclic AMP; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D004837:Epinephrine