Effect of Hypoxic Paracrine Media on Calcium-Regulatory Proteins in Infarcted Rat Myocardium

Background and Objectives: An increase in intracellular calcium concentration due to loss of $Ca^{2+}$ homeostasis triggers arrhythmia or cardiac cell death in the heart. Paracrine factors released from stem cells have beneficial cardioprotective effects. However, the mechanism of modulation of $Ca^{2+}$ homeostasis by paracrine factors in ischemic myocardium remains unclear. Materials and Methods: We isolated rat bone marrow-derived mesenchymal stem cells (MSCs), and prepared paracrine media (PM) from MSCs under hypoxic or normoxic conditions (hypoxic PM and normoxic PM). We induced rat myocardial infarction by left anterior descending ligation for 1 hour, and treated PM into the border region of infarcted myocardium (n=6/group) to identify the alteration in calcium-regulated proteins. We isolated and stained the heart tissue with specific calcium-related antibodies after 11 days. Results: The hypoxic PM treatment increased $Ca^{2+}$-related proteins such as L-type $Ca^{2+}$ channel, sarcoplasmic reticulum $Ca^{2+}$ ATPase, $Na^+/K^+$ ATPase, and calmodulin, whereas the normoxic PM treatment increased those proteins only slightly. The sodium-calcium exchanger was significantly reduced by hypoxic PM treatment, compared to moderate suppression by the normoxic PM treatment. Conclusion: Our results suggest that hypoxic PM was significantly associated with the positive regulation of $Ca^{2+}$ homeostasis in infarcted myocardium.