Astragaloside IV Improved Intracellular Calcium Handling in Hypoxia-Reoxygenated Cardiomyocytes via the Sarcoplasmic Reticulum Ca<sup>2+</sup>-ATPase

Although astragaloside IV, a saponin isolated from <i>Astragalus membranaceus</i>, has been shown to protect the myocardium against ischemia/reperfusion injury, its effect on the status of sarcoplasmic reticulum (SR) Ca²⁺ transport in the injured myocardium remains largely unknown. In this study, we investigated whether in cultured cardiomyocytes subjected to hypoxia and reoxygenation (H/R) administration of astragaloside IV during H/R attenuates the myocardial cell injury and prevents changes in Ca²⁺ handling activities and gene expression of SR Ca²⁺ pump. Cultured cardiomyocytes from neonatal rats were exposed to 6 h of hypoxia followed by 3 h of reoxygenation. Myocyte injury was determined by the release of cardiac troponin I in supernatant. Astragaloside IV significantly inhibited cardiac troponin I release after H/R in a dose-dependent manner. The diastolic [Ca²⁺]_i measured with Fura-2/AM was significantly increased after reoxygenation. Astragaloside IV prevented the rise of diastolic [Ca²⁺]_i and the depression of caffeine-induced Ca²⁺ transients caused by H/R. Furthermore, the observed depressions in SR Ca²⁺-ATPase activity as well as the mRNA and protein expression of SR Ca²⁺-ATPase in hypoxic-reoxygenated cardiomyocytes were attenuated by astragaloside IV treatment. These results suggest that the beneficial effect of astragaloside IV in H/R-induced injury may be related to normalization of SR Ca²⁺ pump expression and, thus, may prevent the depression in SR Ca²⁺ handling.