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Wenting Zhou, Dekang Gan, Gezhi Xu; Electrical Stimulation Suppresses Microglial Activation Induced By Light-damaged Photoreceptors Through Rectifier K+ Channel-dependent Signaling Pathway. Invest. Ophthalmol. Vis. Sci. 2012;53(14):5531.
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To determine the anti-inflammatory effect of electrical stimulation (ES) through suppression of Microglial activation induced by light-reared photoreceptor cells and to explore the underlying mechanism involved in this process.
Sprague-Dawley rats received 1-hour transcorneal electrical stimulation every day up to 3 days after exposing them to intense blue light for 24 hours. Then the immunohistochemistry was used to analyze the activated status of microglia cells in the retina. And the change of IL-1β and TNF-α protein levels was measured by Western blot. Meanwhile, 1-hour of ES was applied to cultivated microglia cells which were previously co-cultured with light damaged cone-derived cell line (661w cells) for 24 hours. Then the whole-cell patch clamp was adopted to detect difference of rectifier K+ current densities receiving ES or not. Real-time PCR was also performed to detect IL-1β and TNF-α mRNA change with or without application of spermine, an inward rectifier K+ channel (IR) blocker or charybdotoxin, a delayed rectifier K+ channel (DR) blocker in various treatment conditions.
A reduced rate of Microglial activation, migration and proliferation in the light exposed rats that received ES was revealed by immunostaining, parallel with downregulated retina levels of IL-1β and TNF-α protein expression. For in vitro study, ES induced larger IR currents but declined DR currents evaluated by patch clamp recordings, which coincided with decreased numbers of ameboid microglia cells. Moreover, IR channel blockade by spermine abolished the anti-inflammatory effect of ES, in which no significant downregulation of IL-1β and TNF-α mRNA levels was observed while DR channel blockade by charybdotoxin didn't.
These results suggest that ES induces diminished microglial activation via upregulation of IR channels while downregulation of DR channels. Thus, ES is further determined to be a novel and potent therapeutic tool of photoreceptor degeneration for its direct anti-inflammatory actions.
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