Fig. 3. NHE-1 activation. A: In agreement with what we have shown previously [14], NHE-1 phosphorylation at serine 703 (estimated by a phospho-Ser 14-3-3 binding motif antibody, "p-14-3-3-BM") was significantly increased by myocardial stretch ("St") compared to non-stretched controls ("Control"), as shown in the original western blots (top) and the averaged data (bottom). Interestingly, this effect was magnified in stretched muscles pre-treated with the p38-MAPK inhibitor, SB202190 ("St+SB"). SB alone did not modify basal NHE-1 phosphorylation (92±6 % of control, n=3). B: Consistently, p38-MAPK inhibition ("SB") significantly increased NHE-1-mediated H⁺ efflux (J_H+) after an acidic challenge (ammonium prepulse), effect that was not observed in muscles pre-treated with the inactive analogous of SB202190, SB202474 (IA). Typical pH_i recordings (top) and averaged initial (maximal) H⁺ efflux (bottom) under all experimental conditions are shown. For the sake of comparison, the best exponential fit for each pH_i recovery from acidosis was superimposed. * indicates p<0.05 vs non-stretched Control, ** indicates p<0.05 vs. St, and # indicates p<0.05 vs. Control acidosis (CA) and IA.