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

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.

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.

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.