Cyclic AMP phosphodiesterase in cloned astrocytoma cells: norepinephrine induces a specific enzyme form.

The soluble supernatant fraction of homogenates of cloned rat astrocytoma cells (linle C-2A) was subjected to polyacrylamide gel electrophoresis. Two peaks of adenosine 3',5'-monophosphate phosphodiesterase activity were found, corresponding to peaks I and IV of a similarly prepared homogenate of rat brain. Incubating cells with norepinephrine (0.3 mullimolar) caused about a threefold increase in the activity of peak IV but no change in peak I. This increase was completely inhibited by prior inclubation with propranolol (0.1 millimnolar), a beta-adrenergic blocking agent, or with cyclohexamnine (40 micromolar). a protein synthesis inhibitor. Induction of a specific phosphodiesterase form by norepinephrine sitggests another feedback control mechanism whereby an organism can prevent the effects of excessive sympathetic activity.