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Transepithelial absorption of exogenous inorganic carbon in the ctenidium of the giant clam, Tridacna squamosa involves a basolateral electrogenic Na+-HCO3- cotransporter 1 that displays light-enhanced gene and protein expression levels
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Type
Article
Citation
Boo, M. V., Chew, S. F., & Ip, Y. K. (2021). Transepithelial absorption of exogenous inorganic carbon in the ctenidium of the giant clam, Tridacna squamosa involves a basolateral electrogenic Na+-HCO3- cotransporter 1 that displays light-enhanced gene and protein expression levels. Coral Reefs, 40, 1849-1865. https://doi.org/10.1007/s00338-021-02142-6
Abstract
Giant clams live in symbiosis with phototrophic dinoflagellates. They need to increase the uptake of inorganic carbon (Ci) from the ambient seawater to support light-enhanced shell formation in the host and photosynthesis in the symbionts during illumination. The ctenidium is the major site of light-enhanced Ci absorption in the fluted giant clam, Tridacna squamosa. Catalyzed by dual-domain carbonic anhydrase, exogenous HCO3− is dehydrated to CO2, which permeates the apical membrane of the ctenidial epithelium and is rehydrated back to HCO3− in the cytoplasm. However, the molecular mechanism that transports cytoplasmic HCO3− through the basolateral membrane to the hemolymph has not been elucidated. We have obtained from the ctenidium of T. squamosa the complete cDNA coding sequence of a homolog of electrogenic Na+–HCO3− cotransporter 1 (NBCe1-like), which comprised 3450 bp, encoding a protein (NBCe1-like) of 1142 amino acids and 128.9 kDa. NBCe1-like had a basolateral localization in epithelial cells covering the ctenidial filament and those surrounding the tertiary water channels. Light exposure led to significant increases in the transcript and protein levels of NBCe1-like/NBCe1-like in the ctenidium of T. squamosa, indicating that NBCe1-like could be involved in the increased transport of cytoplasmic HCO3− across the basolateral membrane into the hemolymph during illumination. Additionally, NBCe1-like might also participate in light-enhanced NO3− absorption in T. squamosa, due to the replacement of aspartate (residue 585) with glutamine. Exogenous NO3− could be absorbed by the ctenidial epithelial cells through the apical H+:NO3− cotransporter (SIALIN) and then transported through the basolateral NBCe1-like to the hemolymph.
Date Issued
2021
Publisher
Springer
Journal
Coral Reefs