Integrative cytological analysis of the effects of Ca2+ and vitamin D3 on extracellular Ca2+ flux and intracellular Ca2+ reserves in the mantle of the pearl oyster (Hyriopsis cumingii Lea)

To examine Ca2+ absorption and transportation in the freshwater pearl oyster, Hyriopsis cumingii Lea, we studied the effects of different levels of either extracellular Ca2+ or 1,25(OH)2D3 on extracellular Ca2+ flux and intracellular Ca2+ concentrations in mantle cells using the non-invasive micro-test technique and laser scanning confocal microscopy. The inner and outer mantle (IM and OM) cells from mussels were cultured and then treated with different concentrations of Ca2+ and 1,25(OH)2D3. Extracellular Ca2+ flux and intracellular Ca2+ reserves were analyzed. The results showed that both extracellular Ca2+ and 1,25(OH)2D3 had significant effects on Ca2+ flux and reserves in mantle cells, especially in IM cells (P < .05). The increase in extracellular Ca2+ concentrations resulted in the conversion of extracellular Ca2+ flux into influx with an increase in flow rate (P < .05). The calcium ion fluorescence intensity of OM cells was higher than that of IM cells (P < .05). 1,25(OH)2D3 addition also significantly increased the influx rate of extracellular Ca2+, especially in IM cells, which were more sensitive to 1,25(OH)2D3 addition and had significantly higher Ca2+ influx rates than did OM cells (P < .05). Fluorescence intensities of intracellular Ca2+ first increased and then decreased with increasing 1,25(OH)2D3 levels. The study showed that IM cells play an important role in absorbing Ca2+ from the environment, while OM cells mainly function in the temporary storage and transportation of Ca2+ in the body. The current results suggested that high levels of extracellular Ca2+ (1.25 mM) or 1,25(OH)2D3 (over 100 IU/L) were favorable for Ca2+ uptake and maintenance in the body.