Effects of 50 Hz extremely low frequency magnetic field on the morphology and function of boar spermatozoa capacitated in vitro

The aim of this study was to evaluate the effect of an acute exposure to a sinusoidal MF-ELF (50 Hz, 1 mT) on the ability of boar mature spermatozoa to acquire the fertilizing competence in vitro. The spermatozoa exposed during the 4 h of incubation to the MF-ELF were evaluated for morphological (surface morphology and acrosome integrity) and functional parameters (cell viability, motility, induction of acrosomal reaction, AR, and the ability to in vitro fertilize oocytes). In parallel, the intracellular Ca2+ levels as well as the major mechanisms of Ca2+ clearance were assessed: Ca-45 intakes and intracellular Ca2+ sequestration by analyzing intracellular Ca2+ elevation induced by thapsigargin or studying mitochondrial function with Mito-Tracker. The MF-ELF exposure did not affect sperm viability and morphology during the first h of incubation when sperm Ca2+ homeostasis were already compromised. First of all, MF-ELF treated spermatozoa showed resting intracellular Ca2+ levels significantly lower than those recorded in controls. This result was dependent on a lower extracellular Ca2+ intake and from the inhibitory role exerted on both intracellular Ca2+ storages. As a consequence, after 1 h of incubation MF-ELF exposed cells displayed a reduced motility, a modest reactivity when coincubated with solubilized zonae pellucidae and a reduction in oocyte penetrating ability. After 2 or 4 h of incubation, in addition, signs of morphological damage appeared on plasma membrane and at acrosomal level. In conclusion, MF-ELF influence negatively spermatozoa first by impairing cell Ca2+ homeostasis then by dramatically affecting sperm morphology and function. [...]