title: Decreased activity of the Na+/H+ exchanger by phosphodiesterase 5A inhibition is attributed to an increase in protein phosphatase activity.
abstract: The beneficial effect of phosphodiesterase 5A inhibition in ischemia/reperfusion injury and cardiac hypertrophy is well established. Inhibition of the cardiac Na(+)/H(+) exchanger (NHE-1) exerts beneficial effects on these same conditions, and a possible link between these therapeutic strategies was suggested. Experiments were performed in isolated cat cardiomyocytes to gain insight into the intracellular pathway involved in the reduction of NHE-1 activity by phosphodiesterase 5A inhibition. NHE-1 activity was assessed by the rate of intracellular pH recovery from a sustained acidic load in the absence of bicarbonate. Phosphodiesterase 5A inhibition with sildenafil (1 μmol/L) did not affect basal intracellular pH; yet, it did decrease proton efflux (J(H); in millimoles per liter per minute) after the acidic load (proton efflux: 6.97±0.43 in control versus 3.31±0.58 with sildenafil; P<0.05). The blockade of both protein phosphatase 1 and 2A with 100 nmol/L of okadaic acid reverted the sildenafil effect (proton efflux: 6.77±0.82). In contrast, selective inhibition of protein phosphatase 2A (1 nmol/L of okadaic acid or 100 μmol/L of endothall) did not (3.86±1.0 and 2.61±1.2), suggesting that only protein phosphatase 1 was involved in sildenafil-induced NHE-1 inhibition. Moreover, sildenafil prevented the acidosis-induced increase in NHE-1 phosphorylation without affecting activation of the extracellular signal-regulated kinase 1/2-p90(RSK) pathway. Our results suggest that phosphodiesterase 5A inhibition decreases NHE-1 activity, during intracellular pH recovery after an acidic load, by a protein phosphatase 1-dependent reduction in NHE-1 phosphorylation.
authors: Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, UNLP, La Plata, Argentina.
authors: Alejandra M
authors: AM
authors: Yeves
authors: Carolina D
authors: CD
authors: Garciarena
authors: Mariela B
authors: MB
authors: Nolly
authors: Gladys E
authors: GE
authors: Chiappe de Cingolani
authors: Horacio E
authors: HE
authors: Cingolani
authors: Irene L
authors: IL
authors: Ennis
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002415:Cats; D002478:Cells, Cultured; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5 / Q000378:metabolism; D003998:Dicarboxylic Acids / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D015151:Immunoblotting; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D019319:Okadaic Acid / Q000494:pharmacology; D058986:Phosphodiesterase 5 Inhibitors; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D010879:Piperazines / Q000494:pharmacology*; D054645:Protein Phosphatase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011522:Protons; D011687:Purines / Q000494:pharmacology; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000378:metabolism; D000068677:Sildenafil Citrate; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D013450:Sulfones / Q000494:pharmacology*
chemical_list: D003998:Dicarboxylic Acids; D004791:Enzyme Inhibitors; D058986:Phosphodiesterase 5 Inhibitors; D010726:Phosphodiesterase Inhibitors; D010879:Piperazines; D011522:Protons; D011687:Purines; D017923:Sodium-Hydrogen Exchangers; D013450:Sulfones; C100030:endothall; D019319:Okadaic Acid; D000068677:Sildenafil Citrate; D038744:Ribosomal Protein S6 Kinases, 90-kDa; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D054645:Protein Phosphatase 1; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5