Turnover of cyclic AMP was studied in intact chicken erythrocytes. Production of cyclic AMP was stimulated by adrenaline and then blocked by propranolol. The decline in the cyclic AMP concentration under these conditions is solely due to its intracellular degradation, whereas efflux of the nucleotide, although existing in these cells, does not contribute significantly to the change in its concentration. Intracellular degradation of cyclic AMP follows a first-order kinetics with a half-life of about 6 min. Similar half-lives were obtained at widely different adrenaline concentrations or when the ration of propranolol to adrenaline was varied by 25-fold. Theoretical equations were applied to calculate the rates of cyclic AMP synthesis and degradation in the intact cells under different experimental conditions. Maximal adrenaline concentrations raise the rate of cyclic AMP synthesis and its steady-state concentration by about 10-fold. The addition of caffeine causes a further 33% increase in intracellular concentration of the nucleotide, which is in good agreement with the theoretical increase computed from its slowed-down degradation.
- © 1979 London: The Biochemical Society