P605Unraveling tight spatiotemporal regulation of 5-HT4 receptor-mediated inotropic effects using targeted FRET-based cAMP sensors

    loading  Checking for direct PDF access through Ovid


Background: We have previously reported that an inotropic response (increase in contractility) to serotonin through 5-HT4 receptors appears in the ventricle of failing rat and human hearts. The inotropic response is ~80% of that to β-adrenergic receptor (β-AR) stimulation in failing rat hearts, yet the increase in cAMP levels is only ~20% compared to β-AR stimulation in cardiac myocytes. As another extreme, EP prostanoid receptor activation has long been considered to yield large increases in myocyte cAMP levels without a positive inotropic response, although some recent data have made this less clear, at least in mouse heart. It thus appears that cAMP produced through stimulation of 5-HT4 receptors and a subset of β-ARs is more tightly coupled to a cardiac inotropic response, e.g. through localization of the produced cAMP closer to the contractile apparatus, compared to EP prostanoid receptors. We have previously found that cAMP produced following 5-HT4 receptor stimulation is degraded by both phosphodiesterase 3 (PDE3) and PDE4, whereas the 5-HT4-mediated inotropic response is primarily limited by PDE3, indicating that localized degradation of cAMP is a primary factor that confines compartmentation of cAMP signaling.

Methods: Experiments were performed on cardiac myocytes from left ventricle from Wistar rats with heart failure 6 weeks after myocardial infarction or sham-operated animals. We measured local concentrations of cAMP in both normal and failing cardiac myocytes using FRET (Fluorescence Resonance Energy Transfer)-based cAMP sensors specifically targeted to subcellular compartments.

Results and conclusion: We find that in failing cardiac myocytes, 5-HT4 receptor stimulation results in a larger increase in cAMP close to the contractile compartment compared to compartments not associated with contraction, whereas β-AR stimulation increases both local and global levels of cAMP. Inhibiting PDE3 enhances both 5-HT4 receptor- and β-AR-mediated increases in cAMP, supporting the notion that PDEs define the contractile compartment. Thus, both production and degradation of cAMP regulating inotropic effects appear to be tightly controlled.

Related Topics

    loading  Loading Related Articles