The selective inhibition of cyclic nucleotide phosphodiesterase isoenzymes from human brain by denbufylline

Abstract

This study was undertaken to characterize adenosine 3′5′cyclic monophosphate (cAMP) and guanosine 3′5′-cyclic monophosphate (cGMP) phosphodiesterases (PDEs) in porcine detrusor smooth muscle and to define their possible role in tension regulation.PDEs were isolated from porcine detrusor homogenate by Q-Sepharose an ion exchange and calmodulin affinity chromatography. The effects of selective inhibitors of CAMP and cCMP PDEs were investigated on isolated PDEs and on carbachol (1 μM) precontracted detrusor strips.Six PDE isoenzymes were isolated by Q-Sepharose anion exchange and calmodulin affinity chromatography: one calmodulin-stimulated PDE (PDE I) which hydrolyzed mainly cGMP, one cGMP-stimulated cAMP PDE (PDE II), two cAMP-specific PDE (PDE IVα and IVβ), and two cGMP-specific PDE (PDE Vα and Vβ). PDE I was potently inhibited in a dose-dependent fashion by papaverine, vinpocetine, and zaprinast; the PDE IVs were potently inhibited by papaverine and rolipram; and the PDE Vs were weakly inhibited by papaverine. In organ bath studies, inhibitors of PDE III (milrinone), IV (rolipram), and V (zaprinast) caused only minor relaxations at high concentrations (200 μM), whereas papaverine and vinpocetine caused relaxations of more than 50%.Our findings support the involvement of cyclic nucleotide metabolism in the regulation of the detrusor smooth muscle tone in the pig and its regulation by PDEs. The weak action of PDE IV and V inhibitors in vitro may be explained by a possible intracellular compartmentalization of such PDEs and the low cyclic nucleotide turnover rate at the conditions used.