REGULATION OF CAMP PHOSPHODIESTERASES BY CYCLIC-NUCLEOTIDES IN RAT PAROTID-GLAND

Approximately 88% of the total cAMP phosphodiesterase (PDE) activity w as detected in the supernatant fraction of the rat parotid homogenate. Mono Q ion-exchange chromatography revealed five main peaks (PDE I, P DE II, PDE III, PDE IV and unknown). A high concentration of cGMP (>1 mu M) 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 I II and IV were activated by treatment with a catalytic subunit of cAMP -dependent protein kinase (A kinase), and H-8, a A kinase inhibitor, i nhibited the activation. Treatment of parotid slices with 1 mu M isopr oterenol stimulated PDE activity by approximately 120%, and 10 mu M pr opranolol inhibited the activation.