Decreased activity of NHE-1 by PDE5A inhibition is due to an increased activity of Protein Phosphatase 1 (PP1).

ALEJANDRA M. YEVES,; CAROLINA D. GARCIARENA; MARIELA B. NOLLY; GLADYS E. CHIAPPE DE CINGOLANI; HORACIO E. CINGOLANI; IRENE L. ENNIS

Orlando, Florida. EE.UU.

Congreso; 2009 Scientific Sessions of The American Heart Association.; 2009

The beneficial effect of phosphodiesterase 5A inhibition in ischemia/reperfusion injury and cardiac hypertrophyis well established. Inhibition of the cardiac Naϩ/Hϩ exchanger (NHE-1) exerts beneficial effects on these sameconditions, and a possible link between these therapeutic strategies was suggested. Experiments were performed inisolated cat cardiomyocytes to gain insight into the intracellular pathway involved in the reduction of NHE-1 activityby phosphodiesterase 5A inhibition. NHE-1 activity was assessed by the rate of intracellular pH recovery from asustained acidic load in the absence of bicarbonate. Phosphodiesterase 5A inhibition with sildenafil (1 ␮mol/L) did notaffect basal intracellular pH; yet, it did decrease proton efflux (JH; in millimoles per liter per minute) after the acidicload (proton efflux: 6.97Ϯ0.43 in control versus 3.31Ϯ0.58 with sildenafil; PϽ0.05). The blockade of both proteinphosphatase 1 and 2A with 100 nmol/L of okadaic acid reverted the sildenafil effect (proton efflux: 6.77Ϯ0.82). Incontrast, selective inhibition of protein phosphatase 2A (1 nmol/L of okadaic acid or 100 ␮mol/L of endothall) did not(3.86Ϯ1.0 and 2.61Ϯ1.2), suggesting that only protein phosphatase 1 was involved in sildenafil-induced NHE-1inhibition. Moreover, sildenafil prevented the acidosis-induced increase in NHE-1 phosphorylation without affectingactivation of the extracellular signal–regulated kinase 1/2-p90RSK pathway. Our results suggest that phosphodiesterase5A inhibition decreases NHE-1 activity, during intracellular pH recovery after an acidic load, by a protein phosphatase1– dependent reduction in NHE-1 phosphorylation.