Selective alteration of Ca2+-dependent and Ca2+-independent cyclic nucleotide phosphodiesterase activity in rat cerebral cortex by cyclic nucleotides and their analogs

The effects of various cyclic nucleotides and cyclic nucleotide analogs on the activity of Ca2+-independent and Ca2+-dependent phosphodiesterases purified from rat cerebral cortex were examined. The order of potency for inhibition of the Ca2+-dependent Enzyme by the various agents was the same using either cAMP or cGMP as substrate with 2'-O-monobutyryl cGMP, cIMP and 2-deoxy cGMP being the most potent. The inhibition of deoxy cGMP using cAMP or cGMP as substrate was competitive, with Ki values of 11 and 13 microM, respectively. In marked contrast, hydrolysis of cAMP or cGMp by the Ca2+-independent Enzyme was stimulated 50-75% by cIMP, deoxy cGMP and N2-monobutyryl cGMP with EC50 values of 7, 20 and 30 microM, respectively. cGMP (EC50, 1.5 microM) produced quantitatively the same degree of stimulation of cAMP hydrolysis by the Ca2+-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 the Ca2+-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 Ca2+-dependent phosphodiesterase and deoxy cAMP in inhibiting the Ca2+-independent Enzyme may provide convenient means to examine specifically these activities in crude extracts from rat cerebral cortex.