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.
Keywords: Antidepressant; Brain-derived neurotrophic factor; Calcium waves; S100A10; Serotonin receptor 4.
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