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Ca²⁺ signaling regulation plays an important role in triggering and/or maintaining atrial fibrillation (AF). Little is known about the relationship of the inositol-1,4,5-triphosphate receptors (InsP₃Rs) and ryanodine receptors (RyRs) in left atrium to chronic AF. In this study, we investigated the expression and function of InsP₃R₁, InsP₃R₂ and RyR₂ in a chronic dog model of AF. AF was induced in 6 dogs by rapid right atrial pacing for 24 weeks, and a sham procedure was performed in 5 dogs (control group). The intact left atrial myocytes were used to examine the expression and function of InsP₃Rs, RyRs by BODIPY^O,R TR-X ryanodine, heparin-fluorescein conjugate, and were stimulated by caffeine, ATP to release Ca²⁺ through RyRs, InsP₃Rs separately. We also assessed the molecular components of left atrial tissue underlying the amount of RyR₂, InsP₃R₁ and InsP₃R₂ determined by RT-PCR, immunohistochemistry and Western blot analysis. In the chronic AF group, the Ca²⁺ released through RyRs is not altered, but the Ca²⁺ released through InsP₃Rs increased significantly. RyR₂ distributed in cytosol of myocytes, cellular membrane; its expression significantly decreased in AF group compared to controls. InsP₃R₁ distributed in cytosol, InsP₃R₂ distributed not only in cytosol, cellular membrane, but also in nuclear envelope and intercalated discs. The InsP₃R₁ and InsP₃R₂ expression significantly increased in chronic AF group compared to controls. These results indicated that in a chronic dog model of AF, the expression and function of RyR₂ down-regulated; on the contrary, the expression and function of InsP₃R₁, InsP₃R₂ up-regulated, and InsP₃R₂ may be the major InsP₃Rs, which regulate intracellular or even intercellular Ca²⁺ signal transmission.

Background: Although soil erosion plays a key role in the carbon cycle, a holistic and mechanistic understanding of the soil erosion process within the cycle is still lacking. The aim of this study was therefore to improve our mechanistic understanding of soil organic carbon (SOC) and soil respiration dynamics through an experiment conducted in an eroding black soil farmland landscape in Northeast China. Results: The depositional profiles store 5.9 times more SOC than the eroding profiles and 3.3 times more SOC than the non-eroding profiles. A linear correlation between the SOC and 137 Cs (Caesium-137) was observed in our study, suggesting that the SOC decreased with increased soil erosion. Furthermore, the fractions of intermediate C and the microaggregate C were lowest at the eroding position and highest at the depositional position. In the depositional topsoil, the input of labile materials plays a promotional role in soil respiration. Conversely, in the subsoil (i.e., below 10 cm), the potential mineralization rates were lowest at the depositional position-due to effective stabilization by physical protection within soil microaggregates. The field results of soil surface respiration also suggest that the depositional topsoil SOC is prone to be mineralized and that SOC at this depositional context is stabilized at subsoil depth. In addition, the high water contents at the depositional position can limit the decomposition rates and stabilize the SOC at the same time. Conclusions:The findings from this study support that a majority of the SOC at footslope is stored within most of the soil profile (i.e., below 10 cm) and submitted to long-term stabilization, and meanwhile support that the depositional profile emits more CO 2 than the summit due to its high amount and quality of SOC.