Activities of 3′: 5′ cyclic nucleotide phosphodiesterases in the superior cervical ganglion of rat: Characterization, compartmentalization and observations in young and old animals

We investigated the presence and features of "low K_m" 3′-5′ cyclic nucleotide phosphodiesterase activity in the homogenates and extracts of rat superior cervical ganglion. The DEAE chromatographic elution profile of a Triton X-100 extract showed two peaks of cAMP phosphodiesterase activity eluted at 280 and 600 mM sodium acetate and two peaks of cGMP phosphodiesterase activity eluted at 300 and at 500 mM sodium acetate. The activity was poorly stimulated by calcium-calmodulin and neither stimulated or inhibited by cGMP. Both cGMP PDE peaks were inhibited by zaprinast, with IC₅₀'s of 1.4 μM and 0.28 μM; their K_m values were 4.4 and 3.8 μM, respectively. These features, together with cGMP binding activity, indicate that both enzymes belong to the phosphodiesterase V family. The K_m values of the first and second cAMP phosphodiesterase peaks were 1.7 and 3.8 μM. Although both peaks displayed a cAMP specific hydrolysis, only the second peak was inhibited by RO 20-1724, with an IC₅₀ of 8 μM. Preganglionic denervation indicated that the bulk of phosphodiesterase activity is localized in ganglion cells. In order to investigate possible effects of aging on the ganglionic function, phosphodiesterase activity was assayed in the ganglia of young (3 months) and old (25 months) male Fisher rats. The chromatographic profiles and kinetic features revealed no significant differences between young and old rats.