Aglianico Grape Pomace Extract Reduces Cardiac Pacemaker Activity by Decreasing Hyperpolarization-Activated Current Density Independently of cAMP Signaling

Grape pomace extract (GPE) from Vitis vinifera L. cv. Aglianico is rich in polyphenols with recognized cardioprotective properties, yet its direct electrophysiological effects on spontaneous cardiac activity have not been previously investigated. Here, we examined the chronotropic effects of GPE using two complementary models: HL-1 cardiomyocytes, assessed by whole-cell patch-clamp and intracellular Ca2+ imaging, and the Drosophila melanogaster larval heart tube, evaluated by optical recording. In HL-1 cells, chronic treatment with 25 µg/mL GPE for 48 h significantly reduced potential spontaneous action frequency and selectively prolonged the diastolic depolarization phase without altering action potential morphology, depolarization-activated currents, or cytosolic Ca2+ homeostasis. GPE reduced the hyperpolarization-activated funny current (If) density without shifting its voltage dependence. GPE-treated cells retained cAMP sensitivity, as both isoproterenol and intracellular 8-Br-cAMP significantly increased If amplitude, while ELISA quantification confirmed that global cAMP levels were unaffected by GPE. In Drosophila larvae, a cAMP-independent myogenic preparation, GPE administered in the diet significantly reduced heart rate. These findings demonstrate that Aglianico GPE exerts a negative chronotropic effect through a mechanism that reduces functional If density without altering cAMP availability or HCN channel voltage dependence, and reveal a cAMP-independent component of action conserved across phylogenetically distant species.