Na\u3csup\u3e+\u3c/sup\u3e/K\u3csup\u3e+\u3c/sup\u3e-ATPase α1 mRNA Expression In the Gill and Rectal Gland of the Atlantic Stingray, \u3ci\u3eDasyatis sabina\u3c/i\u3e, Following Acclimation to Increased Salinity Physiology

Background: The salt-secreting rectal gland plays a major role in elasmobranch osmoregulation, facilitating ion balance in hyperosmotic environments in a manner analogous to the teleost gill. Several studies have examined the central role of the sodium pump Na+/K+-ATPase in osmoregulatory tissues of euryhaline elasmobranch species, including regulation of Na+/K+-ATPase activity and abundance in response to salinity acclimation. However, while the transcriptional regulation of Na+/K+-ATPase in the teleost gill has been well documented the potential for mRNA regulation to facilitate rectal gland plasticity during salinity acclimation in elasmobranchs has not been examined. Therefore, in this study we acclimated Atlantic stingrays, Dasyatis sabina (Lesueur) from 11 to 34 ppt salinity over 3 days, and examined changes in plasma components as well as gill and rectal gland Na+/K+-ATPase α1 (atp1a1) mRNA expression. Results: Acclimation to increased salinity did not affect hematocrit but resulted in significant increases in plasma osmolality, chloride and urea. Rectal gland atp1a1 mRNA expression was higher in 34 ppt-acclimated D. sabina vs. controls. There was no significant change in gill atp1a1 mRNA expression, however mRNA expression of this gene in the gill and rectal gland were negatively correlated. Conclusions: This study demonstrates regulation of atp1a1 in the elasmobranch salt-secreting gland in response to salinity acclimation and a negative relationship between rectal gland and gill atp1a1 expression. These results support the hypothesis that the gill and rectal gland play opposing roles in ion balance with the gill potentially facilitating ion uptake in hypoosmotic environments. Future studies should further examine this possibility as well as potential differences in the regulation of Na+/K+-ATPase gene expression between euryhaline and stenohaline elasmobranch species