THE INHIBITORY EFFECT OF SHAKUYAKUKANZOTO ON K+ CURRENT IN H9c2 CELLS

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Shakuyakukanzoto (shao-yao-gan-cao-tang) is a commonly used Chinese traditional herbal medicine for the treatment of acute pain with muscle cramp. However, its mechanism of action is unclear. We previously reported that a low concentration of Kanzo (licorice) and isoliquiritigenin, a component of licorice, inhibited the potassium (K+) current in H9c2 cells. Therefore, in the present study, we examined the effects of Shakuyakukanzoto, Shakuyaku or Kanzo on the K+ current (IKur) in H9c2 cells. Shakuyakukanzoto inhibited IKur in a concentration-dependent manner. The half-maximal concentration of Shakuyakukanzoto was approximately 1.3 mg/mL and the Hill coefficient was 1.2. The order of potency of inhibiting IKur was Kanzo> Shakuyakukanzoto> Shakuyaku. Glycyrrhizin, a major component of licorice, had no inhibitory effect on IKur. A small interfering RNA experiment indicated that IKur was most likely to be Kv2.1 in H9c2 cells. Our results suggest that Shakuyakukanzoto may normalize intracellular and extracellular K+ balance by inhibiting IKur and reducing K+ efflux, while the Na+-K+ pump promotes K+ influx into myofibers. Consequently, excess K+ may be reduced from external space of myofibers. This may be a part of the Shakuyakukanzoto mechanism for improving muscle pain.