Research reportResveratrol inhibits Na+ currents in rat dorsal root ganglion neurons
Introduction
Resveratrol (trans-3,4′,5-trihydroxystilbene), a polyphenolic antioxidant found in some plants including grapevines, has such beneficial biological effects as neuroprotection, anticancer, anti-inflammation and cardioprotection [27]. Resveratrol suppresses the synthesis of proinflammatory mediators of lipid origin by inhibiting cyclooxygenase (COX) and lipoxygenase pathways [22], [25]. Edema formation associated with both acute and chronic phases of inflammation is reduced by resveratrol with an activity similar to that of indomethacin, a nonsteroidal antiinflammatory drug [19]. Both COX-1 and COX-2 isoforms are inhibited by resveratrol [19], [32], which implies that resveratrol may have an analgesic activity. Indeed, in a model of inflammatory hyperalgesia in which carrageenan was injected into rat hind paw, resveratrol reversed the hyperalgesia [12]. This effect was ascribed to the inhibition of COX-2 or aryl hydrocarbon receptor. In the formalin-induced inflammatory pain, however, resveratrol-induced antinociception was attributed to the inhibition of COX-1 [34].
In addition to the inhibition of lipid metabolism, ion channels appear to participate in the antinociception produced by resveratrol. Resveratrol directly stimulated Ca2+ activated-K+ channel with an increase in open time and a decrease in closed time [24]. The antinociceptive action of resveratrol in the formalin test was prevented by large and small conductance Ca2+ activated-K+ channel blockers and voltage-dependent K+ channel inhibitors, suggesting that opening of these K+ channels may contribute to the resveratrol-induced antinociception [16].
Na+ channels in dorsal root ganglion (DRG) neurons can be separated into two groups by their susceptibility to tetrodotoxin (TTX) [23], [30]. Both TTX-sensitive (TTX-S) and TTX-resistant (TTX-R) Na+ channels are implicated in pain pathways and blockers of the channels can suppress acute, inflammatory and neuropathic pain [1], [38]. A possible contribution of Na+ current inhibition to the resveratrol-induced analgesia has not been examined. In this study, we investigated the effects of resveratrol on TTX-S and TTX-R Na+ currents in acutely dissociated rat DRG neurons using patch-clamp technique. Indeed, resveratrol inhibited two types of Na+ currents in a concentration-dependent manner.
Section snippets
Cell preparation
DRG neurons were prepared from Sprague–Dawley rats, postnatal days 2–7. Rats were anesthetized with ethyl ether and decapitated. Spinal column was opened and ganglia were removed under a dissecting microscope. The ganglia were trimmed of attached fibers in Ca2+, Mg2+-free phosphate-buffered saline (PBS, Sigma, St. Louis, MO). They were incubated at 36 °C first in PBS containing collagenase (0.125% w/v, Type II-S, Sigma) for 15 min and then transferred to PBS containing trypsin (0.25% w/v, Type
Effects of resveratrol on Na+ current amplitude
Na+ current was evoked by a depolarizing pulse to 0 mV from a holding potential of −80 mV every 15 s. Currents recorded in this way are shown in Figs. 1B and C, representing TTX-S and TTX-R Na+ currents, respectively. As well known, TTX-R Na+ current activated and inactivated much more slowly than TTX-S Na+ current. It should be noted that the time scales are different between Figs. 1B and C.
After stabilization of the current, 100 μM resveratrol was applied for 10 min. Resveratrol inhibited two
Discussion
Resveratrol suppressed both TTX-S and TTX-R Na+ currents in rat DRG neurons in a concentration-dependent manner. The apparent dissociation constant was estimated to be 72 μM for TTX-S Na+ current and 211 μM for TTX-R Na+ current, indicating that the former is approximately three times more susceptible to resveratrol than the latter. Besides, in TTX-S Na+ current, but not in TTX-R Na+ current, the activation of the current was suppressed, as demonstrated by depolarizing shift of the G–V curve
Acknowledgment
This work was supported by the Strategic Research Program of Chung-Ang University in 2002.
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