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Figure 3 Effect of tumor necrosis factor-alpha (TNF) (10 ng/ml) on mk2^–/– (KO) and mk2^+/+ (WT) hearts during coronary perfusion under conditions of constant pressure. Data represented by mean ± SEM. (A) Left ventricular developed pressure (LVDP) before and during exposure to TNF. (B) Coronary flow before and during TNF. (C) Upper part shows representative Western blots of total and phosphorylated p38-MAPK and MKK3/6 in hearts exposed to TNF for 15 min. Lower part shows quantitative data expressed in arbitrary units as phosphorylation increase related to total amount for a given protein (mean ± SEM; n = 3), because total p38-MAPK is altered by the mk2 genotype. Consequently, p38-MAPK dual phoshorylation is less pronounced in mk2^–/– than in mk2^+/+. MKK3 is preferentially activated over MKK6 by TNF, with detectable phospho-MKK3/6 signal in both mk2^–/– and mk2^+/+.