β-Adrenergic response is counteracted by extremely-low-frequency pulsed electromagnetic fields in beating cardiomyocytes

Proper beta-adrenergic signaling is indispensable for modulating heart frequency. Studies on extremely-low-frequency pulsed electromagnetic field (ELF-PEMF) effects in the heart beat function are contradictory and no definitive conclusions were obtained so far. To investigate the interplay between ELF-PEMF exposure and beta-adrenergic signaling, cultures of primary murine neonatal cardiomyocytes and of sinoatrial node were exposed to ELF-PEMF and short and long-term effects were evaluated. The ELF-PEMF generated a variable magnetic induction field of 0-6 mT at a frequency of 75 Hz. Exposure to 3 mT ELF-PEMF induced a decrease of contraction rate, Ca2+ transients, contraction force, and energy consumption both under basal conditions and after beta-adrenergic stimulation in neonatal cardiomyocytes. ELFPEMF exposure inhibited beta-adrenergic response in sinoatrial node (SAN) region. ELF-PEMF specifically modulated beta 2 adrenergic receptor response and the exposure did not modify the increase of contraction rate after adenylate cyclase stimulation by forskolin. In HEK293T cells transfected with beta 1 or beta 2 adrenergic receptors, ELF-PEMF exposure induced a rapid and selective internalization of beta 2 adrenergic receptor. The beta-adrenergic signaling, was reduced trough Gi protein by ELFPEMF exposure since the phosphorylation level of phospholamban and the PI3K pathway were impaired after isoproterenol stimulation in neonatal cardiomyocytes. Long term effects of ELF-PEMF exposure were assessed in cultures of isolated cardiomyocytes. ELF-PEMF counteracts cell size increase, the generation of binucleated of cardiomyocytes and prevents the up-regulation of hypertrophic markers after beta-adrenergic stimulation, indicating an inhibition of cell growth and maturation. These data show that short and long term exposure to ELF-PEMF induces a reduction of cardiac beta-adrenergic response at molecular, functional and adaptative levels. Published by Elsevier Ltd.