Expression of Multiple Aquaporin Channels in the Osmoregulatory Tissues of the European Eel (Anguilla anguilla)

During acclimation of eels from freshwater (FW) to seawater (SW), water loses across body surfaces are counteracted by a drinking response, which subsequently involves the uptake of water from the intestine. Duplicate AQP1 aquaporin water channel genes have been isolated from the eel. The first AQP1 isoform was expressed in a wide range of tissues and at high levels in the intestine, which mRNA abundance increased considerably in both yellow and silver developmental stages following SW transfer. Overall higher levels of AQP1 mRNA were found in silver rather than yellow eel intestine. The other eel AQP1 isoform (AQP1 dup) mRNA was found in a smaller range of tissues but its expression was sporadic. AQP1 mRNA was most abundant in the posterior segment of the intestine with intermediate levels in the middle and lower levels in the anterior region of both yellow and silver eels. Significant up-regulation of intestinal AQP1 mRNA expression was found in all segments and both developmental stages. Both yellow and silver eels had similar intestinal AQP1 expression profiles following SW transfer, with mRNA levels slightly decreased after 6 hours followed by increases after 2 days, 7 days or 3-4 months. However, the data also indicated that AQP1 mRNA expression levels reach maximum faster in silver than yellow eels followings SW transfer. The data suggests that AQP1 may play a role in intestinal water uptake following drinking.