“…As a result, under many conditions, the hydrolytic rate of PDEs would be less than maximal and increased cellular cGMP would be predicted to increase hydrolytic rate of these PDEs simply as a result of mass action. PDE2 has low affinity for cGMP (K m Ͼ 10 M), which might suggest limited function in the "physiological" range of cGMP levels found in most cells, but its function has been shown to be physiologically relevant in a number of instances (MacFarland et al, 1991;Bender and Beavo, 2006a;Conti and Beavo, 2007;Surapisitchat et al, 2007;Masood et al, 2008Masood et al, , 2009. PDE1, PDE2, PDE3, and PDE5 have been reported to be present in cardiomyocytes although there are still controversies in this area (see below).…”