PROTEIN-KINASE A-DEPENDENT ACTIVATION OF PDE4 (CAMP-SPECIFIC CYCLIC-NUCLEOTIDE PHOSPHODIESTERASE) IN CULTURED BOVINE VASCULAR SMOOTH-MUSCLECELLS

Incubation of cultured bovine vascular smooth muscle cells (VSMC) with forskolin increased cAMP as measured by an increase in cAMP-dependent protein kinase (PKA) activation (PKA ratio), Forskolin also produced a concentration- and time-dependent increase in activity (3-5-fold wit hin 15 min) of a PDE4 (cAMP-specific cyclic nucleotide phosphodiestera se). The increase in PDE4 activity was not affected by cycloheximide a nd thus not likely due to increased synthesis of the enzyme. Activatio n, which was preserved during partial purification of the enzyme by ch romatography on Sephacryl S-200 and MonoQ, was most likely due to a co valent modification, Incubation of cell homogenates with the catalytic subunit of PKA (PKA(c)) induced a similar to 5-fold activation of PDE 4 with a time course similar to that in intact cells after forskolin a ddition. The forskolin-mediated activation was reversed during incubat ion of homogenates at room temperature for two hours. Addition of PKA( c) resulted in rapid reactivation of PDE4. These data are consistent w ith the hypothesis that rapid, reversible activation of PDE4 in cultur ed VSMC is mediated by PKA.