In light, giant clams can increase rates of shell formation and growth due to their symbiotic relationship with phototrophic zooxanthellae residing extracellularly in a tubular system. Light-enhanced shell formation necessitates increase in the uptake of Ca2+ from the ambient seawater and the supply of Ca2+ through the hemolymph to the extrapallial fluid, where calcification occurs. In this study, the complete coding cDNA sequence of a homolog of voltage-gated calcium channel subunit α1 (CACNA1), which is the pore-forming subunit of L-type voltage-gated calcium channels (VGCCs), was obtained from the ctenidium (gill) of the giant clam, Tridacna squamosa. It consisted of 6081 bp and encoded a 223 kDa polypeptide with 2027 amino acids, which was characterized as the α1D subunit of L-type VGCC. Immunofluorescence microscopy demonstrated that CACNA1 had an apical localization in the epithelial cells of filaments and tertiary water channels in the ctenidium of T. squamosa, indicating that it was well positioned to absorb exogenous Ca2+. Additionally, there was a significant increase in the protein abundance of CACNA1 in the ctenidium of individuals exposed to light for 12 h. With more pore-forming CACNA1, there could be an increase in the permeation of exogenous Ca2+ into the ctenidial epithelial cells through the apical membrane. Taken together, these results denote that VGCC could augment exogenous Ca2+ uptake through the ctenidium to support light-enhanced shell formation in T. squamosa. Furthermore, they support the proposition that light-enhanced phenomena in giant clams are attributable primarily to the direct responses of the host’s transporters/enzymes to light, in alignment with the symbionts’ phototrophic activity.

中文翻译：

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有凹槽的巨蛤的钙吸收，Tridacna squamosa，可能涉及电压门控钙通道亚基 α1 (CACNA1) 的同系物，该亚基具有顶端定位并在蠊中显示出光增强的蛋白质表达

从光看，巨蛤可以提高壳形成和生长的速度，因为它们与存在于细胞外的管状系统中的光养虫黄藻存在共生关系。光增强壳的形成需要增加从周围海水中吸收 Ca2+ 和通过血淋巴向外层液体供应 Ca2+，在那里发生钙化。在这项研究中，电压门控钙通道亚基 α1 (CACNA1) 是 L 型电压门控钙通道 (VGCC) 的成孔亚基的同源物的完整编码 cDNA 序列，是从鲟中获得的。 gill) 的巨蛤，Tridacna squamosa。它由 6081 bp 组成，编码一个 223 kDa 的多肽，有 2027 个氨基酸，是 L 型 VGCC 的 α1D 亚基。免疫荧光显微镜显示 CACNA1 在 T.squamosa 的 ctenidium 的细丝和三级水通道的上皮细胞中具有顶端定位，表明它可以很好地吸收外源性 Ca2+。此外，暴露于光 12 小时的个体在 ctenidium 中的 CACNA1 蛋白质丰度显着增加。随着更多的成孔 CACNA1，外源性 Ca2+ 通过顶膜渗透到 ctenidial 上皮细胞中可能会增加。总之，这些结果表明 VGCC 可以增加外源性 Ca2+ 通过 ctenidium 的吸收，以支持 T.squamosa 中光增强的壳形成。此外，