Seawater carbonate chemistry, mass, length and gene expression of Sepia officinalis during experiments, 2011

The specific transporters involved in maintenance of blood pH homeostasis in cephalopod molluscs have not been identified to date. Using in situ hybridization and immuno histochemical methods, we demonstrate that Na+/K+-ATPase (soNKA), a V-type H+-ATPase (soV-HA), and Na+/HCO3- cotransporter (soNBC) are co-localized in NKA-rich cells in the gills of Sepia officinalis. mRNA expression patterns of these transporters and selected metabolic genes were examined in response to moderately elevated seawater pCO2 (0.16 and 0.35 kPa) over a time-course of six weeks in different ontogenetic stages. The applied CO2 concentrations are relevant for ocean acidification scenarios projected for the coming decades. We determined strong expression changes in late stage embryos and hatchlings, with one to three log2-fold reductions in soNKA, soNBCe, socCAII and COX. In contrast, no hypercapnia induced changes in mRNA expression were observed in juveniles during both short- and long-term exposure. However a transiently increased demand of ion regulatory demand was evident during the initial acclimation reaction to elevated seawater pCO2. Gill Na+/K+-ATPase activity and protein concentration were increased by approximately 15% in during short (2-11 day), but not long term (42 day) exposure. Our findings support the hypothesis that the energy budget of adult cephalopods is not significantly compromised during long-term exposure to moderate environmental hypercapnia. However, the down regulation of ion-regulatory and metabolic genes in late stage embryos, taken together with a significant reduction in somatic growth, indicates that cephalopod early life stages are challenged by elevated seawater pCO2.

截至目前，头足类软体动物体内参与血液pH稳态（blood pH homeostasis）维持的特异性转运蛋白仍未被探明。本研究采用原位杂交（in situ hybridization）与免疫组织化学（immunohistochemical）方法，证实Na+/K+-ATP酶（Na+/K+-ATPase，soNKA）、V型H+-ATP酶（V-type H+-ATPase，soV-HA）以及Na+/HCO3-协同转运蛋白（Na+/HCO3- cotransporter，soNBC）共同定位于真乌贼（Sepia officinalis）鳃内富含Na+/K+-ATP酶的细胞中。本研究针对不同发育阶段的个体，在为期六周的时间进程中，检测了上述转运蛋白与选定代谢基因的mRNA表达模式对中度升高的海水pCO2（0.16与0.35 kPa）的响应情况。本实验设置的CO2浓度与未来数十年预估的海洋酸化情景相匹配。研究发现，晚期胚胎与初孵幼体的基因表达出现显著变化：soNKA、soNBCe、socCAII以及COX的mRNA表达量下调1至3个log2倍数（log2-fold）。与之相反，无论是短期还是长期暴露于高碳酸血症（hypercapnia）环境中，幼体的mRNA表达均未出现高碳酸血症诱导的变化。但在初始适应升高的海水pCO2过程中，离子调节的需求呈现短暂上升的特征。短期暴露（2~11天）后，鳃组织的Na+/K+-ATP酶活性与蛋白浓度均提升约15%，但长期暴露（42天）后未观察到此变化。本研究结果支持如下假说：成年头足类的能量收支在长期暴露于中度环境高碳酸血症时不会受到显著损害。然而，晚期胚胎中离子调节与代谢基因的下调，连同躯体生长的显著减缓，表明头足类的早期生命阶段会受到海水pCO2升高的挑战。