Paradoxical effects of ginkgolide B on cardiomyocyte contractile function in normal and high-glucose environments

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Abstract

Aim

Ginkgo biloba extract is a natural product used widely for cerebral and cardiovascular diseases. It is mainly composed of terpene lactones (ginkgolide A and B) and flavone glycosides (eg quercetin and kaempferol). To better understand the cardiac electromechanical action of Ginkgo biloba extract in normal and diabetic states, this study was designed to examine the effect of ginkgolide B on cardiomyocyte contractile function under normal and high-glucose environments.

Methods

Isolated adult rat ventricular myocytes were cultured for 6 h in a serum-free medium containing either normal (NG; 5.5 mmol/L) or high (HG; 25.5 mmol/L) glucose with or without ginkgolide B (0.5-2.0 μg/mL). Mechanical properties were evaluated using the IonOptix MyoCam system. Contractile properties analyzed included peak shortening (PS), maximal velocity of shortening/relengthening (±dl/dt), time-to-PS (TPS) and time-to-90% relengthening (TR9>0). Levels of essential Ca2+ regulatory proteins sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA2a), phospholamban (PLB) and Na+-Ca2+ exchanger (NCX) were assessed by Western blotting.

Results

Ginkgolide B nullified HG-induced prolongation in TR90. However, ginkgolide B depressed PS, ±dl/dt and shortened TPS in NG and HG cells. Ginkgolide B also prolonged TR90 in NG cells. Western blot analysis revealed that HG upregulated SERCA2a and downregulated PLB expression without affecting that of NCX. Ginkgolide B disrupted the NG-HG response pattern in SERCA2a and NCX without affecting that of PLB.

Conclusion

Ginkgolide B affects cardiomyocyte contractile function under NG or HG environments in a paradoxical manner, which may be attributed to uneven action on Ca2+ regulatory proteins under NG and HG conditions.

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