Calcium-independent activation of calcium ion dependent cyclic nucleotide phosphodiesterase by synthetic compounds: quinazolinesulfonamide derivatives.

Quinazolinesulfonamides are synthetic compounds which calcium-independently stimulate Ca2+-dependent cyclic nucleotide phosphodiesterase. As this activation was observed with 2,4-dipiperidino-6-quinazolinesulfonamides but not with 4-piperidino-6-quinazolinesulfonamides, the activation seems to be dependent on the piperidine residue at the 2 and 4 position of the quinazoline ring, and the extent of hydrophobicity of each compound was thus enhanced. 2,4-Dipiperidino-6-quinazolinesulfonamide activates Ca2+-dependent phosphodiesterase in the absence of Ca2+-calmodulin (CaM). These quinazolinesulfonamides did not further enhance the activity of Ca2+-dependent phosphodiesterase activated by the Ca2+-CaM complex. These compounds are also potent inhibitors of cyclic AMP and GMP phosphodiesterases. CaM antagonists such as N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7), its derivatives, and chlorpromazine and prenylamine inhibited selectively the quinazolinesulfonamide-induced activations of the phosphodiesterase. These quinazolinesulfonamides, in a high concentration, had only a slight stimulatory effect on myosin light chain kinase activity. All these findings suggest that the quinazolinesulfonamides are calcium-independent activators of Ca2+-dependent phosphodiesterase and they are proving to be useful tools for the study of CaM and phosphodiesterase, in vitro.