Calcium absorption in the fluted giant clam, Tridacna squamosa , may involve a homolog of voltage-gated calcium channel subunit α1 (CACNA1) that has an apical localization and displays light-enhanced protein expression in the ctenidium

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 ofT. 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 inT. 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.
Source: Journal of Comparative Physiology B: Biochemical, Systemic, and Environmental Physiology - Category: Physiology Source Type: research