Effects of glycyrrhizin (GLR) and paeoniflorin (PF), depolarizing neuromuscular blockers, on intracellular Ca2+-aequorin luminescence in the presence of or the absence of caffeine were investigated, using directly stimulated diaphragm muscle of mouse. Both GLR and PF decreased Ca2+-aequorin luminescence. The caffeine-induced increase in Ca2+-aequorin luminescence was inhibited by GLR, but not by PF. These results demonstrated that GLR and PF decreased intracellular Ca2+; GLR suppressed Ca2+-releasing from the site of action of caffeine, but PF did not.
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