p11 modulates calcium handling through 5-HT4R pathway in rat ventricular cardiomyocytes.

BACKGROUND: The role of the serotonin receptor 4 (5-HT4R) pathway in cardiac excitation-contraction coupling (ECC) remains unclear. In the brain, induction of the calcium (Ca(2+))-binding protein p11 enhances 5-HT4R translocation and signaling and could therefore be considered as a modulator of the 5-HT4R pathway in the myocardium. p11 expression is increased by brain-derived neurotrophic factor (BDNF) or antidepressant drugs (imipramine). Thus, we investigated whether p11 regulates the 5-HT4R pathway in the heart in physiological conditions or under pharmacological induction and the effects on calcium handling. METHODS AND RESULTS: p11 expression was induced in vivo in healthy Wistar rats by imipramine (10 mg/kg/21 days) and in vitro in left ventricular cardiomyocytes exposed to BDNF (50 ng/ml/8h). Cell shortening and real-time Ca(2+) measurements were processed on field-stimulated intact cardiomyocytes with the selective 5-HT4R agonist, prucalopride (1 µM). Both imipramine and BDNF-induced cardiomyocyte p11 expression unmasked a strong response to prucalopride characterized by an increase of both cell shortening and Ca(2+) transient amplitude compared to basal prucalopride associated with a high propensity to trigger diastolic Ca(2+) events. Healthy rats treated with BDNF (180 ng/day/14 days) exhibited a sustained elevated heart rate following a single injection of prucalopride (0.1 mg/kg) which was not observed prior to treatment. CONCLUSIONS: We have identified a novel role for p11 in 5-HT4R signaling in healthy rat ventricular cardiomyocytes. Increased p11 expression by BDNF and imipramine unraveled a 5-HT4R-mediated modulation of cardiac Ca(2+) handling and ECC associated with deleterious Ca(2+) flux disturbances. Such mechanism could partly explain some cardiac adverse effects induced by antidepressant treatments.

Subendocardial increase in reactive oxygen species production affects regional contractile function in ischemic heart failure.

AIMS: Heart failure (HF) is characterized by regionalized contractile alterations resulting in loss of the transmural contractile gradient across the left ventricular free wall. We tested whether a regional alteration in mitochondrial oxidative metabolism during HF could affect myofilament function through protein kinase A (PKA) signaling. RESULTS: Twelve weeks after permanent left coronary artery ligation that induced myocardial infarction (MI), subendocardial (Endo) cardiomyocytes had decreased activity of complex I and IV of the mitochondrial electron transport chain and produced twice more superoxide anions than sham Endo and subepicardial cells. This effect was associated with a reduced antioxidant activity of superoxide dismutase and Catalase only in MI Endo cells. The myofilament contractile properties (Ca(2+) sensitivity and maximal tension), evaluated in skinned cardiomyocytes, were also reduced only in MI Endo myocytes. Conversely, in MI rats treated with the antioxidant N-acetylcysteine (NAC) for 4 weeks, the generation of superoxide anions in Endo cardiomyocytes was normalized and the contractile properties of skinned cardiomyocytes restored. This effect was accompanied by improved in vivo contractility. The beneficial effects of NAC were mediated, at least, in part, through reduction of the PKA activity, which was higher in MI myofilaments, particularly, the PKA-mediated hyperphosphorylation of cardiac Troponin I. INNOVATION: The Transmural gradient in the mitochondrial content/activity is lost during HF and mediates reactive oxygen species-dependent contractile dysfunction. CONCLUSIONS: Regionalized alterations in redox signaling affect the contractile machinery of sub-Endo myocytes through a PKA-dependent pathway that contributes to the loss of the transmural contractile gradient and impairs global contractility.