The effect of rolipram and denbufylline. (A) Rolipram (0.3 μmol/L) was preincubated with cAS-PDE samples for 2 minutes and then 8-BDB-TcAMP (5 mmol/L) was added (□). The data (○) represents samples treated only with 8-BDB-TcAMP (5 μmol/L). (B) Denbufylline (0.5 μmol/L) was preincubated for 2 minutes and then 8-BDB-TcAMP (8 mmol/L) was added (○). The data (□) represent inactivation of cAS-PDE by 8 mmol/L 8-BDB-TcAMP. The timed aliquots were diluted 20,000-fold and activity determined in triplicate.