Ca²⁺ activated and pH sensitive cyclic AMP phosphodiesterase in the nervous system of the mollusc Pleurobranchaea

Regulation of cyclic AMP through its synthesis is known to be important in modulating the activity of molluscan neurons; however, no data exists regarding the regulation of cyclic AMP degradation. We find that cyclic AMP phosphodiesterase (PDE) activity in homogenates of the nervous system of the mollusc Pleurobranchea is significantly stimulated by calcium ion. Ca²⁺ stimulation is suppressed by the calmodulin antagonist trifluoperazine (TFP), indicating resemblance to the Ca²⁺-calmodulin PDEs of mammalian neurons. Ca²⁺ also accentuates the pH sensitivity of PDE. The qualities of Ca²⁺ and pH sensitivity of PDE are fitted into a model for cAMP regulation of neuronal activity in an identified feeding command neuron; the postulated role of PDE is consistent with effects of cAMP, TFP, and pH on the neuron's activity.