Selective alteration of Ca + -dependent and Ca 2+ -independent cyclic nucleotide phosphodiesterase activity in rat cerebral cortex by cyclic nucleotides and their analogs

Abstract

The effects of various cyclic nucleotides and cyclic nucleotide analogs on the activity of Ca 2+ -independent and Ca2+ -dependent phosphodiesterases purified from rat cerebral cortex were examined. The order of potency for inhibition of the Ca 2+ -dependent enzyme by the various agents was the same using either cAMP or cGMP as substrate with 2′- O-monobutyryl cGMP, clMP and 2-deoxy cGMP being the most potent. The inhibition by deoxy cGMP using cAMP or cGMP as substrate was competitive, with K i values of 11 and 13 μM, respectively. In marked contrast, hydrolysis of cAMP or cGMP by the Ca 2+ -independent enzyme was stimulated 50–75% by cIMP, deoxy cGMP and N 2-monobutyryl cGMP with EC 50 values of 7, 20 and 30 μM, respectively, cGMP (EC 50, 1.5 μ M) produced quantitatively the same degree of stimulation of cAMP hydrolysis by the Ca 2+ -independent phosphodiesterase and the activation was not additive with that of deoxy cGMP. Of the other derivatives examined, 2′- O-monobutyryl cAMP and 2′-deoxy cAMP were the most potent inhibitors of cAMP hydrolysis by tbe Ca 2+ -independent enzyme and were 30–60-times more effective in inhibiting cAMP hydrolysis as compared to cGMP hydrolysis. The specificity of K + in inhibiting the activity of the Ca 2+ -dependent phosphodiesterase and deoxy cAMP in inhibiting the Ca 2+ -independent enzyme may provide convenient means to examine specifically these activities in crude extracts from rat cerebral cortex.