CHUNG, K.F.*; LIN, H.C.; Tunghai University; Tunghai University: Osmoregulation and Na, K-ATPase Expressions in Osmoregulatory Organs of Scylla paramamosain
Scylla paramamosain is a euryhaline marine crab that can regulate its hemolymph osmolality actively and survive in a wide range of salinity. In order to reveal the relationship between environmental salinity and its osmoregulatory organs, we investigated the expressions of Na, K-ATPase among these organs, including anterior gills, posterior gills, antennal glands and midgut. It is suggested that different Na, K-ATPase isoforms exist in anterior and posterior gills, which main function is respiration and osmoregulation, respectively. But according to our cDNA sequencing of Na, K-ATPase α-subunit in this study, no isoform was found in these four osmoregulatory organs studied. Its full-length cDNA contains 3866 bp nucleotides that encode a complete open reading frame of 1039 amino acids. The hemolymph osmolality of the crab changed immediately after transferred to different salinities and reached a new steady state within 3 days. Therefore, it is a hyperhypo-osmoregulator. It was until the 7th day after transfer that the mRNA level increased not only in the posterior gills from 5 ppt treatment, but also in the anterior gills, posterior gills and antennal glands from 45 ppt. This increase in 5 ppt treatment may later lead to the increase of enzyme activity on day 14. Indeed, upon 14 days after transfer, the enzyme activity of the posterior gills in 5 ppt was significantly higher than those in the other two salinity treatments. But no difference was found in the protein level among salinities. In conclusion, the posterior gills played the most important role in osmoregulation when the crabs were in diluted seawater and its increase in Na, K-ATPase activity may result from an increased gene transcription and/or an mRNA translation.
