The role of voltage-gated Ca 2+ channels in neurite growth of cultured chromaffin cells induced by extremely low frequency (ELF) magnetic field stimulation

Abstract

The ion Ca2+ has been shown to play an important role in a wide variety of cellular functions, one of them being related to cell differentiation in which nerve growth factor (NGF) is involved. Chromaffin cells obtained from adrenals of 2- to 3-day-old rats were cultured for 7 days. During this time, these cells were subjected to the application of either NGF or extremely low frequency magnetic fields (ELF MF). Since this induced cell differentiation toward neuronal-like cells, the mechanism by which this occurred was studied. When the L-Ca2+ channel blocker nifedipine was applied simultaneously with ELF MF, this differentiation did not take place, but it did when an N-Ca2+ channel blocker was used. In contrast, none of the Ca2+ channel blockers prevented differentiation in the presence of NGF. In addition, Bay K-8644, an L-Ca2+ channel agonist, increased both the percentage of differentiated cells and neurite length in the presence of ELF MF. This effect was much weaker in the presence of NGF. [3H]-noradrenaline release was reduced by nifedipine, suggesting an important role for L-Ca2+ channels in neurotransmitter release. Total high voltage Ca2+ currents were significantly increased in ELF MF-treated cells with NGF, but these currents in ELF MF-treated cells were more sensitive to nifedipine. Amperometric analysis of catecholamine release revealed that the KCl-induced activity of cells stimulated to differentiate by ELF MF is highly sensitive to L-type Ca2+ channel blockers. A possible mechanism to explain the way in which the application of magnetic fields can induce differentation of chromaffin cells into neuronal-like cells is proposed.

Effects of Acute and Chronic Low Frequency Electromagnetic Field Exposure on PC12 Cells during Neuronal Differentiation

“…The lack of significant effect induced by ELF-EMFs, was also supported by the fact that GAP43 and MAP2, neuronal cytoscheletal markers, levels appeared similar in exposed cells to those of control ones. These results are apparently in contrast with the data already published [6,21,24,42] it should be considered that different ELF-EMF intensities and cell models (even if of the same phenotype) were reported.…”

“…Over the past few years, a lot of data showed that ELF-EMFs exposure can induce modifications of intracellular Ca 2+ levels that can be related to different physiological mechanisms: i.e. differentiation of chromaffin cells into neuronal-like cells [21]; cell death by apoptosis induced by several agents in different human cell systems [66]; and functional modifications of cells of the immune system [67,68]. All of these effects, and many more others, can be attributed to modifications to the Ca 2+ homeostasis by ELF-EMF exposure across different mechanisms, such as the involvement of P2Y membrane receptors [69]; the activation of mechanically operated stretch-activated Ca 2+ channels [70]; and the enhancement of the expression of voltage-gated Ca 2+ channels [20].…”

“…In previous studies, it has been found that exposure to ELF-EMFs increases proliferation and inhibits programmed cell death in human neuroblastoma and rat pituitary cells [20], on the other hand, in rat chromaffin cells and in neural stem cell ELF-EMFs promoted neurogenesis and neuronal differentiation [21,22].…”

Induction of Neuritogenesis in PC12 Cells by a Pulsed Electromagnetic Field via MEK-ERK1/2 Signaling

“…While electromagnetic fields, including pulsed electromagnetic fields (PEMFs), are considered a noninvasive way to promote and align nerve regeneration (Schimmelpfeng et al, 2005), their mode of action at the cellular and molecular levels is unclear. Previous studies indicate that the biological effects of PEMFs, with or without NGF, on neuronal or neuron-like cells appear to be dependent on the usage of a PEMF (Morgado et al, 1998;Schimmelpfeng et al, 2005;Zhang et al, 2006). Few studies have investigated the molecular mechanisms of intracellular signaling in PC12 cells subjected to PEMF stimulation alone.…”

Neuronal differentiation of chromaffin cells in vitro, induced by extremely low frequency magnetic fields or nerve growth factor: A histological and ultrastructural comparative study

“…The mechanisms whereby ELFMF induces differentiation in chromaffin cells are not clearly understood. However, recent experiments conducted in our laboratory have shown that dehydropyridine-sensitive voltage-gated-L-Calcium channels appear to be involved (Morgado-Valle et al, 1998).…”