Modulation of Zebrafish Heart Rate by Alternating Magnetic Fields With Frequencies Close to Heart Rhythm

Extremely low-frequency magnetic fields (ELF-MF) up to 100 μT exhibit impacts on physiological processes, including heart function. The mechanisms underlying the influence of these fields on fish heart rates remain insufficiently explored. We assumed that the direct impact of ELF-MF with a frequency close to the heart rate could entrain oscillatory processes responsible for autonomously maintaining heart rhythm in zebrafish embryos. Embryos' heart rates ranged from 1.44 to 3 Hz depending on age, and ELF-MF with frequencies precisely matched, 10% higher, or lower than the heart rate were applied. Additionally, embryos experienced ELF-MF with amplitudes varying by an order of magnitude. Almost all tested ELF-MF induced an increased heart rate effect. This effect was the most pronounced when the exposure occurred earlier during ontogenesis. Fields with frequencies close to the heart rate did not entrain cardiac contractions in zebrafish embryos. A significant negative correlation between heart rate increase and ELF-MF frequency was observed for ELF-MF with amplitudes of 1.98–3.2 μT and 46.8 μT but not 30 μT. Probable molecular mechanisms underlying these effects are discussed in terms of magnetic influence on radical pairs within biochemical oscillating processes.