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

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

Aarhus

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

Abstract Background/Aims: Phosphodiesterase 5A inhibition by Sildenafil (SIL) decreases cardiacNa+/H+ exchanger (NHE1) phosphorylation/activity byactivating phosphatase PP2A. We propose that p38MAPK could participate as asignaling mediator in the cascade of events triggered by SIL.Methods: NHE1activity was indirectly assessed by Na+-dependent pHirecovery induced by sustained acidosis (SA) of isolated rat papillary muscles. ERK1/2,p38MAPK and NHE1 phosphorylation were determined. Results: Theincrease in NHE1 activity triggered by SA was significantly blunted in presenceof SIL. Inhibition of p38MAPK activity with SB202190 reversed the inhibitoryeffect of SIL. None of these interventions had a significant impact on basal pHisuggesting that their actions would take place only under SA condition. AsSA-induced NHE1 hyperactivity could be attributable to an increased inphosphorylation at Ser703 residue, changes in NHE1 phosphorylation status wereassayed revealing that SIL-induced dephosphorylation in NHE1 was reversed with SB.Furthermore, SB addition itself did not affect basal pHi, NHE1 hyperactivityor its phosphorylation state after SA. On the other hand, p38MAPK activation bysodium arsenite (5umol/L, Ars) or more specifically by Anisomycin (20 umol/L, Aniso)inhibited the acidosis-induced NHE1 hyperactivity clearly resembling the effectof SIL on the exchanger. In addition, the effect of Ars on NHE1 activity wascompletely reverted by SB. Inmunoblot analysis of cardiac samples subjected to SAshowed that SIL treatment but not the acidic challenge itself, increased p38MAPK.Respect of the kinases upstream NHE1, the acidosis-mediated increase in ERK1/2phosphorylation was not modified by SIL or SB minimizing a possiblecompensatory effect of SB over SIL. We have shown previously that phosphatasePP2A activation is responsible of the reduced NHE1 activity after SILtreatment. Interestingly, PP2A inhibition (1 nmol/L Okadaic Acid) reverted Arseffect on NHE1 activity. Conclusion: Ourresults strongly suggest that phosphodiesterase 5A inhibition by SIL promotes ap38MAPK-mediated PP2A activation that lead to a negative modulation of NHE1activity.