Localization of aquaporin-3 proteins in the bovine rumen

摘要

Urea nitrogen salvaging is a crucial mechanism thatruminants have evolved to conserve nitrogen. Facilitativeurea transporter-B proteins are known to be involvedin urea transport across the rumen epitheliumand thus efficiently facilitate the urea nitrogen salvagingprocess. Recently, functional studies have suggestedthat aquaglyceroporin transporters might also play asignificant role in ruminal urea transport and aquaporin-3 (AQP3) protein has previously been detected inrumen tissue. In this current study, we investigated thespecific localization of AQP3 transporters in the bovinerumen. First, end-point reverse-transcription PCR experimentsconfirmed strong AQP3 expression in bothbovine rumen and kidney. Immunoblotting analysisusing 2 separate anti-AQP3 antibodies detected AQP3protein signals at 25, 32, and 42–45 kDa. Further immunolocalizationstudies showed AQP3 protein locatedin all the layers of rumen epithelium, especially in thestratum basale, and in the basolateral membranes ofkidney collecting duct cells. These data confirm thatAQP3 transporters are highly abundant within thebovine rumen and appear to be located throughout theruminal epithelial layers. The physiological significanceof the multiple AQP3 proteins detected and their locationis not yet clear, hence further investigation is requiredto determine their exact contribution to ruminalurea transport.