Gingerol, a novel cardiotonic agent, activates the Ca2+-pumping ATPase in skeletal and cardiac sarcoplasmic reticulum

Abstract Gingerol, isolated as a potent cardiotonic agent from the rhizome of ginger, stimulated the Ca 2+ -pumping activity of fragmented sarcoplasmic reticulum (SR) prepared from rabbit skeletal and dog cardiac muscles. The extravesicular Ca 2+ concentrations of the heavy fraction of the fragmented SR (HSR) were measured directly with a Ca 2+ electrode to examine the effect of gingerol on the SR. Gingerol (3–30 μM) accelerated the Ca 2+ -pumping rate of skeletal and cardiac SR in a concentration-dependent manner. The rate of 45 Ca 2+ uptake of HSR was also increased markedly by 30 μM gingerol without affecting the 45 Ca 2+ efflux from HSR. Furthermore, gingerol activated Ca 2+ -ATPase activities of skeletal and cardiac SR (EC 50 , 4 μM). The activation of SR Ca 2+ -ATPase activity by gingerol (30 μM) was completely reversed by 100-fold dilution with the fresh saline solution. Kinetic analysis of activating effects of gingerol suggests that the activation of SR Ca 2+ -ATPase is uncompetitive and competitive with respect to Mg · ATP at concentrations of 0.2–0.5 mM and above 1 mM, respectively. Kinetic analysis also suggests that the activation by gingerol is mixed-type with respect to free Ca 2+ and this enzyme is activated probably due to the acceleration of enzyme-substrate complex breakdown. Gingerol had no significant effect on sarcolemmal Ca 2+ -ATPase, myosin Ca 2+ -ATPase, actin-activated myosin ATPase and cAMP-phosphodiesterase activities, indicating that the effect of gingerol is rather specific to SR Ca 2+ -ATPase activity. Gingerol may provide a valuable chemical tool for studies aimed at clarifying the regulatory mechanisms of SR Ca 2+ -pumping systems and the causal relationship between the Ca 2+ -pumping activity of SR and muscle contractility.