• Aude Carillion, Sarah Feldman, Cheng Jiang, Fabrice Atassi, Na Na, Nathalie Mougenot, Sophie Besse, Jean-Sébastien Hulot, Bruno Riou, and Julien Amour.
• From the Sorbonne Universités UPMC Univ Paris 06, UMR INSERM-UPMC 1166, Paris, France (A.C., S.F., C.J., F.A., N.M., J.-S.H., B.R., J.A.); Department of Anesthesiology and Critical Care Medicine (A.C., J.A.), Department of Emergency Medicine and Surgery (N.N., B.R.), and Department of Pharmacology (J.-S.H.), Hôpital Pitié-Salpêtrière, Assistance Publique-Hôpitaux de Paris, Paris, France; Université de Reims Champagne-Ardenne and Department of Anesthesiology and Critical Care Medicine, Robert Debré Hospital, Reims, France (A.C.); Wuhan University, Wuhan, The People's Republic of China (C.J.); UMR INSERM 902 Université Evry Val d'Essone, Evry, France (S.B.); and Université Paris-Descartes, Paris, France (S.B.).
• Anesthesiology. 2015 Feb 1;122(2):334-42.

BackgroundIn the senescent heart, the positive inotropic response to β-adrenoceptor stimulation is reduced, partly by dysregulation of β1- and β3-adrenoceptors. The multidrug resistance protein 4 (MRP4) takes part in the control of intracellular cyclic adenosine monophosphate concentration by controlling its efflux but the role of MRP4 in the β-adrenergic dysfunction of the senescent heart remains unknown.MethodsThe β-adrenergic responses to isoproterenol were investigated in vivo (stress echocardiography) and in vitro (isolated cardiomyocyte by Ionoptix with sarcomere shortening and calcium transient) in young (3 months old) and senescent (24 months old) rats pretreated or not with MK571, a specific MRP4 inhibitor. MRP4 was quantified in left ventricular homogenates by Western blotting. Data are mean ± SD expressed as percent of baseline value.ResultsThe positive inotropic effect of isoproterenol was reduced in senescent rats in vivo (left ventricular shortening fraction 120 ± 16% vs. 158 ± 20%, P < 0.001, n = 16 rats) and in vitro (sarcomere shortening 129 ± 37% vs. 148 ± 35%, P = 0.004, n = 41 or 43 cells) as compared to young rats. MRP4 expression increased 3.6-fold in senescent compared to young rat myocardium (P = 0.012, n = 8 rats per group). In senescent rats, inhibition of MRP4 by MK571 restored the positive inotropic effect of isoproterenol in vivo (143 ± 11%, n = 8 rats). In vitro in senescent cardiomyocytes pretreated with MK571, both sarcomere shortening (161 ± 45% vs. 129 ± 37%, P = 0.007, n = 41 cells per group) and calcium transient amplitude (132 ± 25% vs. 113 ± 27%, P = 0.007) increased significantly.ConclusionMRP4 overexpression contributes to the reduction of the positive inotropic response to β-adrenoceptor stimulation in the senescent heart.

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