Assessment of selective inhibition of rat cerebral cortical calcium-independent and calcium-dependent phosphodiesterases in crude extracts using deoxycyclic AMP and potassium ions.
The effects of various inhibitors on the activity of calcium-independent and calcium-dependent phosphodiesterases from rat cerebral cortex were examined. While the agents varied greatly in their relative potency, each was found to be approximately equipotent in inhibiting the calcium-dependent hydrolysis of either cyclic AMP or cyclic GMP. In contrast, the inhibitors displayed a marked substrate specificity for the calcium-independent enzyme with ratios of IC50 values for inhibition of cyclic GMP hydrolysis when compared to cyclic AMP hydrolysis in decreasing order being: ZK 62711 (much greater than 100) greater than Ro 20-1724 (much greater than 25) papaverine (13) greater than 7-benzyl IBMX (4) greater than quercetin and kaempferol (2). The differential selectivity of the inhibitors for the two enzymes was most pronounced for ZK 62711 and Ro 20-1724 which were at least 25-100-times more potent in inhibiting the calcium-independent hydrolysis of cyclic AMP when compared to the calcium-dependent hydrolysis of cyclic AMP. In contrast, 7-benzyl IBMX, kaempferol and quercetin were 8-100-times more effective as inhibitors of cyclic GMP hydrolysis by the calcium-dependent phosphodiesterase while 7-benzyl IBMX and trimazosin displayed a similar enzyme selectivity using cyclic AMP as substrate. With the exception of papaverine, all agents were competitive inhibitors of the calcium-dependent phosphodiesterase. The type of inhibition observed with the calcium-independent enzyme was dependent on the substrate employed. The specificity of potassium ions in inhibiting the activity of the calcium-dependent phosphodiesterase and deoxycyclic AMP in inhibiting the calcium-independent enzyme was found to provide a convenient means to assess the effects of agents on these activities in crude extracts of cerebral cortex.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002540:Cerebral Cortex / Q000187:drug effects / Q000201:enzymology*; D000242:Cyclic AMP / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D006152:Cyclic GMP / Q000378:metabolism; D005260:Female; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains
D010726:Phosphodiesterase Inhibitors; C018892:2'-deoxy cyclic AMP; D000242:Cyclic AMP; D010727:Phosphoric Diester Hydrolases; D006152:Cyclic GMP; D011188:Potassium; D002118:Calcium