Phosphodiesterase isoenzymes in human ureteral smooth muscle: Identification, characterization, and functional effects of various phosphodiesterase inhibitors in vitro

Phosphodiesterases (PDE) are key enzymes regulating intracellular cyclic nucleotide metabolism and, thus, contraction and relaxation of the muscle. At present, five different families of isoenzymes of PDE exist that show a distinct species-specific and organ-specific distribution. The aim of the present study was to analyze the PDE isoenzymes present in the human ureter and to evaluate the functional effects of isoenzyme-specific inhibitors in this tissue. Normal ureteral tissue was obtained during radical nephrectomies, homogenized, centrifuged, and the supernatant fraction was separated using DEAE-Sephacel anion-exchange chromatography. PDE assay was then performed and the isoenzymes characterized on the basis of their kinetic characteristics and their sensitivity to allosteric modulators and inhibitors. In vitro, longitudinal ureteral strips as well as ureteral rings were precontracted, and different selective and nonselective PDE inhibitors were added incrementally. Three different PDE isoenzymes were identified: PDE I (Ca/calmodulin-stimulated), PDE II (cyclic guanosine monophosphate-stimulated), and PDE IV (cyclic adenosine monophosphate-specific). All PDE inhibitors relaxed the strips dose-depen-dently with an EC50 of 30 µM for papaverine, 40 µM for zaprinast, 25 µM for quazinone, and 0.1 µM for rolipram. The existence of three different PDE isoenzymes was shown in this study. The ureter-relaxing effect of the PDE IV inhibitor at low concentrations, combined with its low effect on the systemic circulatory parameters, may open a possibility of using selective PDE IV inhibitors in the treatment of ureteral colics or ureteral stonesa.