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Novel bUT-B2 urea transporter isoform is constitutively activated

¹Faculty of Life Sciences, The University of Manchester, Manchester, UK; and ²School of Biology and Environmental Science, University College Dublin, Dublin, Ireland

Submitted 6 April 2009 ; accepted in final form 22 May 2009

Our previous studies have detailed a novel facilitative UT-B urea transporter isoform, bUT-B2. Despite the existence of mouse and human orthologs, the functional characteristics of UT-B2 remain undefined. In this report, we produced a stable MDCK cell line that expressed bUT-B2 protein and investigated the transepithelial urea flux across cultured cell monolayers. We observed a large basal urea flux that was significantly reduced by known inhibitors of facilitative urea transporters; 1,3 dimethylurea (P < 0.001, n = 17), thionicotinamide (P < 0.05, n = 11), and phloretin (P < 0.05, n = 9). Pre-exposure for 1 h to the antidiuretic hormone vasopressin had no effect on bUT-B2-mediated urea transport (NS, n = 3). Acute vasopressin exposure for up to 30 min also failed to elicit any transient response (NS, n = 9). Further investigation confirmed that bUT-B2 function was not affected by alteration of intracellular cAMP (NS, n = 4), intracellular calcium (NS, n = 3), or protein kinase activity (NS, n = 4). Finally, immunoblot data suggested a possible role for glycosylation in regulating bUT-B2 function. In conclusion, this study showed that bUT-B2-mediated transepithelial urea transport was constitutively activated and unaffected by known regulators of renal UT-A urea transporters.

UT-B2 isoform; protein expression; rumen

This article has been cited by other articles:

				N. L. Simmons, A. S. Chaudhry, C. Graham, E. S. Scriven, A. Thistlethwaite, C. P. Smith, and G. S. Stewart Dietary regulation of ruminal bovine UT-B urea transporter expression and localization J Anim Sci, October 1, 2009; 87(10): 3288 - 3299. [Abstract] [Full Text] [PDF]