Vol. 280, Issue 2, 1043-1050, 1997

Evidence that the Organic Cation/H⁺ Exchanger in the Brush Border Membrane of Dog Kidney Is a 41-kDa Protein¹

Janice S. Gilsdorf, James F. Rebbeor² and Peter D. Holohan

Department of Pharmacology, SUNY Health Science Center at Syracuse, Syracuse, New York

Organic cation (OC⁺)/H⁺ exchangers are found in several mammalian tissues and in numerous organisms. In the kidney OC⁺/H⁺ exchange activity is localized to the brush border membrane of the proximal tubule cells of the nephron and is believed to be responsible for the efflux of numerous xenobiotics from the tubule cell into the tubular fluid. The objective of the present study was to identify the OC⁺/H⁺ exchanger in brush border membrane vesicles isolated from dog kidney by photoaffinity labeling. The results show that [³H]azidopine is an ideal photoaffinity labeling reagent; in the dark it binds reversibly, but irreversibly after photoactivation. The photoaffinity labeling reaction is efficient, specific and sensitive. Our findings are consistent with the conclusions that a 41-kDa protein is the exchanger and that it is present at a concentration of 780 ± 140 fmol/mg membrane protein (n = 4). A 49-kDa protein is labeled to some extent as well. The relationship between the 41- and 49-kDa proteins has not been resolved.