NHE-1 INHIBITION BY SILDENAFIL IS DUE TO PHOSPHATASE ACTIVATION

CAROLINA MASSARUTTI; ROMINA G. DÍAZ; HORACIO E. CINGOLANI; NÉSTOR G. PÉREZ

Buenos Aires, Argentina

Congreso; XVII Meeting de la Internacional Society for Herat Research (ISHR) Latin American Section en conjunto con el XXVII Congreso Nacional de Cardiología; 2009

We suggested that increased protein kinase G (PKG) activity by sildenafil (S) inhibits NHE-1. To further characterize the mechanism involved in this effect, NHE-1 activity was evaluated by the initial (maximal) H+ efflux (JH+ in mM/min) after an acid load (ammonium prepulse) in the absence of bicarbonate in Wistar rat papillary muscles. Phosphodiesterase-5A (PDE5A) was inhibited with 1uM S. S did not modify pHi recovery after an acute acid load (JH+: 1.01±0.13 in control vs. 0.95±0.13 in S) but promoted drastic effects after 10 min of sustained acidosis (JH+: 3.01±0.14 control vs. 0.40±0.15 S, P<0.05). This effect was mimicked by inhibiting the MEKK pathway with 10 uM U0126 (JH+: 0.62±0.13, P<0.05 vs. control). Okadaic acid (1 nM) and endothall (100 uM) non-specific and specific PP2A inhibitors respectively reverted S effect (JH+: 2.95±0.16 okadaic and 3.00±0.16 endothall) suggesting that PP2A was involved in the depressant effect of S on NHE-1. In conclusion, S induced NHE-1 inhibition was only manifested after sustained acidosis and appears to result from PP2A-mediated NHE-1 dephosphorylation. This may explain the beneficial effects of increasing PKG activity in different myocardial pathologies that involve exacerbated NHE-1 activation.