Regulation of cAMP phosphodiesterases by cyclic nucleotides in rat parotid gland

Approximately 88% of the total cAMP phosphodiesterase (PDE) activity was detected in the supernatant fraction of the rat parotid homogenate. Mono Q ion-exchange chromatography revealed five main peaks (PDE I, PDE II, PDE III, PDE IV and unknown). A high concentration of cGMP (> 1 microM) was necessary to activate PDE II, whereas PDE III was inhibited by cGMP at a concentration that was 1,000 times lower (100 pM). PDEs III and IV were activated by treatment with a catalytic subunit of cAMP-dependent protein kinase (A kinase), and H-8, a A kinase inhibitor, inhibited the activation. Treatment of parotid slices with 1 microM isoproterenol stimulated PDE activity by approximately 120%, and 10 microM propranolol inhibited the activation.