Expression of SLC 4A11 protein in mouse and rat medulla: a candidate transporter involved in outer medullary ammonia recycling

SLC 4A11 is a multifunctional membrane transporter involved with H + transport, NH 3 and alkaline pH stimulated H + transport, and water transport. The role of SLC 4A11 in the kidney is not well understood. A prior study has shown that in murine kidney, SLC 4A11/LacZ staining is primarily in the long‐looped descending thin limb ( DTL ) as determined by colocalization with aquaporin 1 ( AQP 1), a protein that is expressed in some, but not all, descending thin limb segments. Using a previously characterized polyclonal antibody, we demonstrate the selective expression of SLC 4A11 in the upper DTL s (which are AQP 1‐positive) in the outer medulla and inner medulla with little or no expression in the lower DTL s (which are AQP ‐1‐null). SLC 4A11 also colocalized with AQP 1 and the urea transporter UT ‐B in the mouse descending vasa recta, but was absent in mouse and rat ascending vasa recta. Mouse, but not rat, outer medullary collecting duct cells also labeled for SLC 4A11. Our results are compatible with the hypothesis that in the inner stripe of the outer medulla, SLC 4A11 plays a role in the countercurrent transport of ammonia absorbed from the outer medullary thick ascending limb and secreted into the long‐looped DTL s. SLC 4A11 can potentially modulate the rate of ammonia transport in the mouse outer medullary collecting duct. Our data suggest functionally unique SLC 4A11 pathways in mouse and rat and complement previous studies of DTL Na + , urea and water permeability indicating that the upper and lower DTL s of long‐looped nephrons are functionally distinct.