PORCINE DETRUSOR CYCLIC-NUCLEOTIDE PHOSPHODIESTERASE ISOENZYMES - CHARACTERIZATION AND FUNCTIONAL-EFFECTS OF VARIOUS PHOSPHODIESTERASE INHIBITORS IN-VITRO

Objectives. This study was undertaken to characterize adenosine 3'5'-c yclic monophosphate (cAMP) and guanosine 3'5'-cyclic monophosphate (cG MP) phosphodiesterases (PDEs) in porcine detrusor smooth muscle and to define their possible role in tension regulation. Methods. PDEs were isolated from porcine detrusor homogenate by Q-Sepharose anion exchang e and calmodulin affinity chromatography. The effects of selective inh ibitors of cAMP and cGMP PDEs were investigated on isolated PDEs and o n carbachol (1 mu M) precontracted detrusor strips. Results. Six PDE i soenzymes were isolated by O-Sepharose anion exchange and calmodulin a ffinity chromatography: one calmodulin-stimulated PDE (PDE I) which hy drolyzed mainly cGMP, one cGMP-stimulated cAMP PDE (PDE II), two cAMP- specific PDE (PDE IV alpha and IV beta), and two cGMP-specific PDE (PD E V alpha and V beta). PDE I was potently inhibited in a dose-dependen t fashion by papaverine, vinpocetine, and zaprinast; the PDE IVs were potently inhibited by papaverine and rolipram; and the PDE Vs were wea kly inhibited by papaverine. In organ bath studies, inhibitors of PDE III (milrinone), IV (rolipram), and V (zaprinast) caused only minor re laxations at high concentrations (200 mu M), whereas papaverine and vi npocetine caused relaxations of more than 50%. Conclusions. Our findin gs support the involvement of cyclic nucleotide metabolism in the regu lation of the detrusor smooth muscle tone in the pig and its regulatio n by PDEs. The weak action of PDE IV and V inhibitors in vitro may be explained by a possible intracellular compartmentalization of such PDE s and the low cyclic nucleotide turnover rate at the conditions used.