PT - JOURNAL ARTICLE AU - Irina G. Rybalkina AU - Xiao-Bo Tang AU - Sergei D. Rybalkin TI - MULTIPLE AFFINITY STATES OF cGMP-SPECIFIC PDE (PDE5) FOR SILDENAFIL INHIBITION DEFINED BY cGMP-DEPENDENT AND cGMP-INDEPENDENT MECHANISMS AID - 10.1124/mol.109.062299 DP - 2010 Jan 19 TA - Molecular Pharmacology PG - mol.109.062299 4099 - http://molpharm.aspetjournals.org/content/early/2010/01/19/mol.109.062299.short 4100 - http://molpharm.aspetjournals.org/content/early/2010/01/19/mol.109.062299.full AB - cGMP specific phosphodiesterase (PDE5) has become a target for drug development for the treatment of a number of physiological dysfunctions, affected by changes in the cGMP/PKG signaling pathway. PDE5 has two highly homologous regulatory domains, GAF-A and GAF-B. Previously we showed that PDE5 could be converted from a low activity (non-activated) state to a high activity state upon cGMP binding to the GAF-A domain with higher sensitivities towards sildenafil (Rybalkin et al., 2003). Here we investigated if sildenafil sensitivity of PDE5 could be modified by cGMP independent mechanisms. Individually expressed recombinant GAF-A and GAF-B proteins were tested for their ability to modulate full-length recombinant PDE5 affinity to sildenafil. The GAF-A domain protein had the most dramatic effect on the affinity of the non-activated recombinant PDE5 for sildenafil, revealing much higher sensitivity to sildenafil inhibition. The apparent affinity for sildenafil increased from the nM range to the pM range, providing evidence for the presence of a "super-high" sensitivity state of PDE5 for sildenafil inhibition. In human platelet higher sensitivity of PDE5 for sildenafil inhibition has been detected after blocking cGMP-binding sites of the GAF-A domain. Thus our data demonstrate that high sensitivity of PDE5 for sildenafil can be obtained not only through cGMP induced activation of PDE5, but also through cGMP independent modulation of PDE5 in the non-activated state, possibly through protein/protein interaction. Furthermore, data suggest that non-activated PDE5 with "super" high affinities for sildenafil inhibition may be responsible for therapeutic effects of chronic treatments with low doses of PDE5 inhibitors.The American Society for Pharmacology and Experimental Therapeutics