BIOCHEMICAL AND PHARMACOLOGICAL CHARACTERIZATION OF CYCLIC-NUCLEOTIDEPHOSPHODIESTERASE IN AIRWAY EPITHELIUM

According to their respective elution order, specificity for cAMP and cGMP, their sensitivity to calmodulin, and their modulation by cGMP an d rolipram, four cyclic nucleotide phosphodiesterases (PDE) were separ ated from the cytosol: PDE I (calmodulin-sensitive), PDE II (stimulate d by cGMP, PDE IV (cGMP specific-PDE and inhibited by rolipram) and PD E V (cGMP specific). PDE IV (K-m = 1.4 mu M) was competitively inhibit ed by rolipram (K-i = 1.2 mu M) whereas PDE V (K-m = 0.83 mu M) was co mpetitively inhibited by zaprinast in the mu molar range (K-i = 0.12 m u M). Moreover the microsomal fraction contained three PDE isoforms: P DE II, PDE III (inhibited by cGMP or indolidan) and PDE IV. These resu lts show that cAMP degradation in cytosolic and membrane fractions is modulated by cGMP and selectively inhibited by rolipram and, in additi on, by indolidan in membrane fractions.