p38MAPK activation plays a crucial role in the signaling pathway that links phosphodiesterase 5A inhibition and NHE1 inactivation

ESCUDERO DS; PÉREZ NG; BREA MS; DIAZ RG; MORGAN PE

Sandbjerg Estate

Congreso; ACTA Physiologica International Symposium - 49th Sandbjerg Meeting on Membrane Transport 2017; 2017

ACTA Physiologica International Symposium

Background/Aims: Phosphodiesterase 5A inhibition by Sildenafil (SIL) decreases cardiac Na+/H+ exchanger (NHE1) phosphorylation/activity by activating phosphatase PP2A. We propose that p38MAPK could participate as a signaling mediator in the cascade of events triggered by SIL.Methods: NHE1 activity was indirectly assessed by Na+-dependent pHi recovery induced by sustained acidosis (SA) of isolated rat papillary muscles. ERK1/2, p38MAPK and NHE1 phosphorylation were determined. Results: The increase in NHE1 activity triggered by SA was significantly blunted in presence of SIL. Inhibition of p38MAPK activity with SB202190 reversed the inhibitory effect of SIL. None of these interventions had a significant impact on basal pHi suggesting that their actions would take place only under SA condition. As SA-induced NHE1 hyperactivity could be attributable to an increased in phosphorylation at Ser703 residue, changes in NHE1 phosphorylation status were assayed revealing that SIL-induced dephosphorylation in NHE1 was reversed with SB. Furthermore, SB addition itself did not affect basal pHi, NHE1 hyperactivity or its phosphorylation state after SA. On the other hand, p38MAPK activation by sodium arsenite (5umol/L, Ars) or more specifically by Anisomycin (20 umol/L, Aniso) inhibited the acidosis-induced NHE1 hyperactivity clearly resembling the effect of SIL on the exchanger. In addition, the effect of Ars on NHE1 activity was completely reverted by SB. Inmunoblot analysis of cardiac samples subjected to SA showed that SIL treatment but not the acidic challenge itself, increased p38MAPK. Respect of the kinases upstream NHE1, the acidosis-mediated increase in ERK1/2 phosphorylation was not modified by SIL or SB minimizing a possible compensatory effect of SB over SIL. We have shown previously that phosphatase PP2A activation is responsible of the reduced NHE1 activity after SIL treatment. Interestingly, PP2A inhibition (1 nmol/L Okadaic Acid) reverted Ars effect on NHE1 activity. Conclusion: Our results strongly suggest that phosphodiesterase 5A inhibition by SIL promotes a p38MAPK-mediated PP2A activation that lead to a negative modulation of NHE1 activity.