doi:10.1016/j.brainres.2007.11.047 
Copyright © 2007 Elsevier B.V. All rights reserved.
Research Report
Effects of a polyacetylene from Panax ginseng on Na+ currents in rat dorsal root ganglion neurons
Sang Jin Choia, Tae Hoon Kima, Yong Kyoo Shina, Chung Soo Leea, Mijung Parkb, Hyun Sun Leec and Jin-Ho Songa, 
, 
aDepartment of Pharmacology, Chung-Ang University, College of Medicine, 221 Heuksuk-Dong, Dongjak-Ku, Seoul 156-756, Republic of Korea
bDepartment of Visual Optics, Seoul National University of Technology, 172 Gongreung-Dong, Nowon-Ku, Seoul 139-743, Republic of Korea
cNatural Medicine Research Center, Korea Research Institute of Bioscience and Biotechnology, 52 Oun, Yusong, Taejon 305-333, Republic of Korea
Accepted 28 November 2007.
Available online 4 December 2007.
References and further reading may be available for this article. To view references and further reading you must
purchase this article.
Abstract
The root of ginseng (Panax ginseng) has been used as a traditional medicine in the far east countries since ancient times. Ginseng extracts produce analgesia among other various biologically beneficial effects. A polyacetylenic compound, (9R,10S)-epoxyheptadecan-4,6-diyn-3-one (EHD), has been isolated from ginseng extract, whose biological activity is largely unknown. Voltage-gated Na+ channels in primary sensory neurons play important roles in pain perception. We investigated the effects of EHD on tetrodotoxin-sensitive (TTX-S) and tetrodotoxin-resistant (TTX-R) Na+ currents in acutely dissociated rat dorsal root ganglion neurons. EHD inhibited both Na+ currents in a concentration-dependent manner with an equal potency (Kd values were both 14.3 μM). The activation voltage was not affected by EHD in either type of Na+ current. However, EHD accelerated the inactivation of both Na+ currents and produced a hyperpolarizing shift of the steady-state inactivation curve. In addition EHD suppressed the maximal Na+ current at negative holding potentials at which the channels are relieved from inactivation. Thus EHD appears to bind both resting and inactivated channels. The recovery from inactivation of both Na+ currents was also slowed by EHD. EHD inhibition of TTX-S Na+ current but not TTX-R Na+ current was frequency-dependent. This is the first report that a polyacetylene from ginseng inhibits Na+ currents in primary sensory neurons. EHD by inhibiting Na+ currents may contribute to the ginseng analgesia.
Keywords: Dorsal root ganglion; Na+ current; Panax ginseng; Polyacetylene; Tetrodotoxin-resistant; Tetrodotoxin-sensitive
Abbreviations: DMSO, dimethylsulfoxide; DRG, dorsal root ganglion; EHD, (9R,10S)-epoxyheptadecan-4,6-diyn-3-one; TTX-R, tetrodotoxin-resistant; TTX-S, tetrodotoxin-sensitive
Fig. 1. EHD inhibition of Na+ currents in DRG neurons. (A) Time course of Na+ current inhibition by EHD (10 μM). Currents were elicited by depolarizing steps of 10-ms (○, TTX-S) or 40-ms (●, TTX-R) duration to 0 mV from a holding potential of − 80 mV at 15-s intervals. EHD was applied for 10 min. (B, C) Typical TTX-S (B) and TTX-R (C) Na+ current traces before and after EHD treatment for 5, and 10 min. A, n = 8; B, n = 8.
Fig. 2. Concentration–response relationship for EHD inhibition of Na+ currents. Currents were elicited by depolarizing steps of 10-ms (○, TTX-S) or 40-ms (●, TTX-R) duration to 0 mV from a holding potential of − 80 mV. Current amplitude at 10-min application of EHD (IEHD) was normalized to control current (Icontrol) and plotted against the concentration of EHD. Every measurement was carried out in a different cell. The means of the measurements were fitted with the Hill equation to yield the smooth lines in the figure. TTX-S, n = 8–10; TTX-R, n = 8–9.
Fig. 3. Effects of EHD on the activation of Na+ currents. (A, B) Examples of current–voltage (I–V) relationship for TTX-S (A) and TTX-R (B) Na+ currents before (open symbols) and after (filled symbols) treatment with EHD (10 μM) for 10 min. Membrane potential was held at − 90 mV (A) or − 80 mV (B), and currents were evoked with test pulses (A, 10 ms; B, 40 ms) to potentials ranging from − 55 mV to + 50 mV in 5-mV increments. (C) Conductance–voltage (G–V) relationships derived from I–V data. Conductance was normalized with respect to the maximal conductance (Gmax) at + 20 mV and plotted against the test potential (TTX-S, n = 7; TTX-R, n = 8). Curves were drawn after fit with a Boltzmann function. ○, TTX-S, control; ●, TTX-S, EHD; □, TTX-R, control; ▪, TTX-R, EHD.
Fig. 4. Effects of EHD on the steady-state inactivation of Na+ currents. Membrane potential was held at − 100 mV and an inactivating pre-pulse of 10 s was given between − 120 mV and − 40 mV in 10-mV increments, which was immediately followed by a depolarizing pulse (A, 10 ms; B, 40 ms) to 0 mV. (A, B) Examples of TTX-S (A) and TTX-R (B) Na+ current families obtained by the protocol before and after treatment with EHD (10 μM) for 10 min. Pre-pulse potentials are indicated for comparison. (C) Current (I) normalized to a maximal control current (Imax) was plotted against the pre-pulse potential (TTX-S, n = 8; TTX-R, n = 7). Curves were drawn after fit with a Boltzmann function. ○, TTX-S, control; ●, TTX-S, EHD; □, TTX-R, control; ▪, TTX-R, EHD.
Fig. 5. Effects of EHD on the recovery of Na+ currents from inactivation. Two identical pulses of 10-ms (A, TTX-S) or 40-ms (B, TTX-R) duration to 0 mV from a holding potential of − 100 mV were separated by an inter-pulse (− 100 mV) duration of increasing amount of time. The protocol was run before and after treatment with EHD (10 μM) for 10 min. Current in response to the second pulse was normalized and plotted against the inter-pulse duration in logarithmic scale (A, n = 8; B, n = 9). Curves were drawn after fit with exponential functions. ○, TTX-S, control; ●, TTX-S, EHD; □, TTX-R, control; ▪, TTX-R, EHD.
Fig. 6. Frequency-dependent inhibition of TTX-S Na+ current by EHD. Twenty repetitive pulses (A, TTX-S, 10 ms; B, TTX-R, 40 ms) to 0 mV from a holding potential of − 80 mV were delivered at 1 and 10 Hz, before and after treatment with EHD (10 μM) for 10 min. Current normalized to the first pulse current was plotted against the pulse number (A, n = 10; B, n = 6). Curves were obtained by fitting mean data with the sum of two exponentials. ○, control, 1 Hz; ●, EHD, 1 Hz; □, control, 10 Hz; ▪, EHD, 10 Hz.
Table 1.
Effects of EHD on the inactivation kinetics of Na+ currents
Currents were evoked at 0 mV (TTX-S, 10 ms; TTX-R, 40 ms) from a holding potential of − 80 mV. EHD (10 μM) was applied for 10 min. The time constant for the current decay fitted with a single exponential function was measured. 
P < 0.01, P < 0.001 compared with control. n = 8 for both currents.
Table 2.
Boltzmann parameters for Na+ currents
Activation and steady-state inactivation curves were constructed as described in the text. Vg0.5 and Vh0.5 refer to the potential at which current is 50% activated or inactivated, respectively, and kg and kh are slope factors. Parenthesis indicates the number of the cells used. Cells were treated with 10 μM EHD for 10 min. P < 0.01, P < 0.001 compared with the spontaneous shift in solvent only (DMSO 0.1%, v/v).
Abstract
Purchase PDF (339 K)
E-mail Article
Add to my Quick Links
Cited By in Scopus (0)
Purchase PDF (423 K)
