Excess glutamate and Ca2+ influx into neurons exacerbate brain damage such as ischemia. Astrocytes at the site of damage proliferate and attenuate the glutamate- and Ca2+-induced neuronal damage by removing excess glutamate and Ca2+ through the N-methyl-D-aspartate (NMDA) glutamate receptor and the L-type Ca2+ channel, respectively. Fibroblasts are commonly mobilized to the site of damage, probably supporting the restoration process. Notably, fibroblasts express the L-type voltage-sensitive Ca2+ channel, but not central nervous system-specific NMDA glutamate receptor. We examined if electric pulse stimulation (EPS) was capable of inducing NMDA receptor on fibroblasts by way of Ca2+ channel activation, so that they could potentially have a neuroprotective role. To activate L-type Ca2+ channel, we delivered electric pulse to cultured NIH3T3 mouse fibroblasts. EPS of 20 V with a pulse duration of 2 msec at a frequency of 1 Hz for more than 1 h up to 24 h successfully introduced Ca2+ into NIH3T3 fibroblasts as detected by Fluo-4AM calcium imaging, which was totally inhibited by a L-type Ca2+ channel inhibitor, verapamil. Remarkable expression of NMDA receptor mRNA in the fibroblasts after 24-h EPS was demonstrated by RT-PCR. Verapamil treatment during EPS totally abrogated the EPS-induced NMDA receptor mRNA expression. To the best of our knowledge, this is the first report showing that electric pulse is able to induce sustained Ca2+ influx via L-type Ca2+ channel in a non-excitatory fibroblast, which leads to the expression CNS-specific NMDA receptor mRNA. Neuroprotective role of NMDA receptor induced in fibroblasts needs to be further examined.
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