Effect of the ginsenoside Rb1 on the spontaneous contraction of intestinal smooth muscle in mice.
OBJECTIVE
To investigate the effect and the possible mechanism of ginsenoside Rb1 on small intestinal smooth muscle motility in mice.


METHODS
Intestinal smooth muscle strips were isolated from male ICR mice (5 wk old), and the effect of ginsenoside Rb1 on spontaneous contraction was recorded with an electrophysiolograph. The effect of ginsenoside Rb1 on ion channel currents, including the voltage-gated K⁺ channel current (IK(V)), calcium-activated potassium channel currents (IK(Ca)), spontaneous transient outward currents and ATP-sensitive potassium channel current (IK(ATP)), was recorded on freshly isolated single cells using the whole-cell patch clamp technique.


RESULTS
Ginsenoside Rb1 dose-dependently inhibited the spontaneous contraction of intestinal smooth muscle by 21.15% ± 3.31%, 42.03% ± 8.23% and 67.23% ± 5.63% at concentrations of 25 μmol/L, 50 μmol/L and 100 μmol/L, respectively (n = 5, P < 0.05). The inhibitory effect of ginsenoside Rb1 on spontaneous contraction was significantly but incompletely blocked by 10 mmol/L tetraethylammonium or 0.5 mmol/L 4-aminopyridine, respectively (n = 5, P < 0.05). However, the inhibitory effect of ginsenoside Rb1 on spontaneous contraction was not affected by 10 μmol/L glibenclamide or 0.4 μmol/L tetrodotoxin. At the cell level, ginsenoside Rb1 increased outward potassium currents, and IK(V) was enhanced from 1137.71 ± 171.62 pA to 1449.73 ± 162.39 pA by 50 μmol/L Rb1 at +60 mV (n = 6, P < 0.05). Ginsenoside Rb1 increased IK(Ca) and enhanced the amplitudes of spontaneous transient outward currents from 582.77 ± 179.09 mV to 788.12 ± 278.34 mV (n = 5, P < 0.05). However, ginsenoside Rb1 (50 μmol/L) had no significant effect on IK(ATP) (n = 3, P < 0.05).


CONCLUSIONS
These results suggest that ginsenoside Rb1 has an inhibitory effect on the spontaneous contraction of mouse intestinal smooth muscle mediated by the activation of IK(V) and IK(Ca), but the K(ATP) channel was not involved in this effect.
Scientific Research Station for Post-doctoral Studies, Post-doctoral Research Centre, Zhongshan Affiliated Hospital, Guangzhou University of Traditional Chinese Medicine, Zhongshan 528400, Guangdong Province, China.
Lei
L
Xu
Sui-Ping
SP
Huang
D000818:Animals; D004305:Dose-Response Relationship, Drug; D005765:Gastrointestinal Agents / Q000494:pharmacology*; D036145:Ginsenosides / Q000494:pharmacology*; D007421:Intestine, Small / Q000187:drug effects* / Q000502:physiology; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D009119:Muscle Contraction / Q000187:drug effects* / Q000502:physiology; D009130:Muscle, Smooth / Q000187:drug effects* / Q000502:physiology; D018408:Patch-Clamp Techniques
D005765:Gastrointestinal Agents; D036145:Ginsenosides; C442759:ginsenoside Rb1