Molecular characterization of an epithelial Ca²⁺ channel-like gene from crayfish Procambarus clarkii

This study describes the cloning, sequencing and functional characterization of an epithelial Ca²⁺ channel (ECaC)-like gene isolated from antennal gland (kidney) of the freshwater crayfish Procambarus clarkii. The fulllength cDNA consisted of 2687 bp with an open reading frame of 2169 bp encoding a protein of 722 amino acids with a predicted molecular mass of 81.7 kDa. Crayfish ECaC had 76-78% identity at the mRNA level (80-82% amino acid identity) with published fish sequences and 56-62% identity at the mRNA level (52-60% amino acid identity) with mammalian ECaCs. Secondary structure of the crayfish ECaC closely resembled that of cloned ECaCs. Postmolt ECaC expression was exclusively restricted to epithelia associated with Ca ²⁺ influx and was virtually undetectable in non-epithelial tissues (eggs, muscle). Compared with expression levels in hepatopancreas, expression in gill was 10-fold greater and expression was highest in antennal gland (15-fold greater than in hepatopancreas). Compared with baseline expression levels in intermolt stage, expression of ECaC in antennal gland increased 7.4- and 23.8-fold, respectively, in pre- and postmolt stages of the molting cycle. This increase was localized primarily in the labyrinth and nephridial canal, regions of the antennal gland associated with renal Ca²⁺ reabsorption. The ECaC in crayfish appears to be expressed in epithelia associated with unidirectional Ca²⁺ influx and relative expression is correlated with rate of Ca²⁺ influx.