Phosphodiesterase inhibition in ventricular cardiomyocytes from guinea‐pig hearts

Abstract

The present study compared the cyclic nucleotide phosphodiesterase (PDE) activities in cardiomyocytes and ventricular cardiac tissue from guinea‐pigs. The aim of the study was to determine whether PDE activities in ventricular tissue accurately reflect the isoenzymes present in cardiomyocytes. In homogenates of cardiomyocytes and multicellular ventricular tissue, four distinct soluble PDE activities could be separated by DEAE‐sepharose chromatography. In multicellular cardiac tissue as well as in cardiomyocyte preparations, adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) PDE isoenzymes I‐IV were comparable in terms of substrate affinities, and inhibition or stimulation by guanosine 3′:5′‐cyclic monophosphate (cyclic GMP). However, in cardiomyocytes the Vmax values of PDE I‐IV were lower by a factor of about 2 to 7 and the basal activities were lower by a factor of about 3 to 5 as compared to multicellular cardiac tissue. To investigate whether the PDE I‐IV activities were similarly inhibited by PDE inhibitors in both preparations, we studied the effects of 3‐isobutyl‐1‐methylxanthine (IBMX), UD‐CG 212 Cl (2‐(4‐hydroxy‐phenyl)‐5‐(5‐methyl‐3‐oxo‐4,5‐dihydro‐2H‐6‐pyridazinyl)benzimidazole HCl) and rolipram. UD‐CG 212 Cl was a selective PDE III inhibitor in cardiomyocytes (IC50 0.3 μmol l−1) and in ventricular tissue (IC50 value 0.1 μmol l−1). Rolipram selectively inhibited PDE IV in cardiomyocytes (IC50 1.4 μmol ml−1) and in ventricular tissue (IC50 1.1 μmol l−1) whereas IBMX was a nonselective PDE inhibitor in both preparations. It is concluded that the PDE isoenzymes I‐IV from multicellular ventricular tissue can be used as a representative system for investigating PDE inhibiting properties of PDE inhibitors in the myocardium since comparable PDE isoenzymes I‐IV exist in guinea‐pig ventricular cardiomyocytes and multicellular ventricular tissue.

Myocardial Phosphodiesterases and Regulation of Cardiac Contractility in Health and Cardiac Disease

“…Bovine cardiac PDE2 has a molecular weight of 240 kDa and can hydrolyse both cAMP and cGMP with similar rates. Likewise, cytosolic PDE2 exhibits similar cAMP and cGMP substrate specificity in rat [60], guinea-pig [33,59] and dog [33] ventricular tissue. However, cytosolic PDE2 preferentially hydrolyses cGMP in rabbit [44], porcine [58] and human [55][56][57][58]70] myocardium.…”

“…PDE2 activity was localised to sarcolemma, mostly at cell-to-cell junctions, as well as to sarcomeric Z-line [75]. On the other hand, only cytosolic PDE2 activity was identified by anion exchange chromatography in guinea-pig [41,56,59], rat [44,60], rabbit [44], human [56] and bovine [46,69] myocardium.…”

“…PDE3 cAMP V max values were shown to be 5-10-fold higher as compared to cGMP in bovine [46], guinea-pig [59], porcine [58] and human [55,58] ventricular tissue. PDE3 activity is effectively inhibited by cGMP with K i value of about 0.06-0.6 μM [30,44,46,61,65].…”

“…Indeed, although PDE1 activity was found in homogenates of rat cardiac ventricles, it was missing in isolated ventricular myocytes [60]. On the other hand, PDE1 activity was found in isolated ventricular myocytes of guinea-pig [59] and hamster [66] suggesting species-related differences in distribution profile of this PDE isoform. PDE1 activity is regulated by protein kinases-mediated phosphorylation [27,28,67].…”

“…PDE1 is Ca 2+ /calmodulin-activated isoenzyme hydrolyzing both cAMP and cGMP with similar substrate specificity in human [35,[55][56][57][58], dog [33], rabbit [44] and guinea-pig [33,59] myocardial tissue. However, PDE1 preferentially hydrolyses cGMP in rat [60] and bovine [46,61] myocardium.…”