Five phosphodiesterase isozymes were separated from the supernatant of pig aortic smooth muscle homogenates, using DEAE-Toyopearl 650S chromatography in the presence of 0.1 mM Ca2+ followed by re-chromatography in the absence of Ca2+ and affinity chromatography on immobilized rolipram or cGMP. Type I (calmodulin-dependent family) preferentially hydrolysed cGMP and its activity was stimulated by calmodulin. Type II (cGMP-stimulated family), which had not yet been identified in aortic smooth muscle, hydrolysed both cGMP and cAMP. Its cAMP hydrolysis was stimulated by 10 muM cGMP. Type III (cGMP-inhibited family) and IV (cAMP-specific family) preferentially hydrolysed cAMP. The cAMP hydrolytic activity of Type III was inhibited by cGMP, but that of Type IV was not. Type V (cGMP-specific family) preferentially hydrolysed cGMP and its activity did not depend on calmodulin. The inhibition of all five phosphodiesterase isozymes by various phosphodiesterase inhibitors was investigated, and the potency and selectivity of each phosphodiesterase inhibitor discussed.
