The role of cyclic nucleotide phosphodiesterase in the inhibition of cyclic AMP accumulation by carbachol and phosphatidate.

Abstract

The possibility that activation of cyclic 3':5'-nucleotide phosphodiesterase is a component of muscarinic inhibition of cyclic AMP accumulation was investigated in WI-38 fibroblasts. At 0.2 to 20 microM, 1-isoamyl-3-isobutylxanthine, an inhibitor of fibroblast phosphodiesterase activity, attenuated the fall in WI-38 cyclic AMP content seen in response to 1 microM carbachol. The inhibitory effect of carbachol on WI-38 cyclic AMP metabolism was also suppressed by the inclusion of 0.1 to 10 microM trifluoperazine in cell incubation media. Exposure of WI-38 cultures to 1 microM carbachol was associated with elevated phosphodiesterase activity in the corresponding broken cell preparations. Both 1-isoamyl-3-isobutylxanthine and trifluoperazine interfered with the ability of 10 microM phosphatidate to mimic carbachol-inhibition of WI-38 cyclic AMP accumulation. Fibroblast calmodulin-dependent phosphodiesterase preparations were activated by micromolar dispersions of phosphatidate. This action of the phospholipid did not appear to require calcium and was blocked by trifluoperazine. These data lend support to the notion that increased cyclic nucleotide phosphodiesterase activity is at least partially responsible for the fall in WI-38 cyclic AMP levels seen in response to cholinergic stimulation. The results also suggest that the effects of cholinergic agents on WI-38 cyclic AMP hydrolysis may be related to changes in phospholipid metabolism, notably the accumulation of phosphatidate.