Abstract
Nitric oxide (NO) generated by neuronal nitric oxide synthase (nNOS) in kidney macula densa (MD) cells functions to vasodilate the afferent arteriole and blunts regulation of tubuloglomerular feedback (TGF). Experiments were performed to examine the effect of NaCl changes in extracellular solution on the NO production from the established mouse macula densa (NE-MD) cells in culture. nNOS protein expression was assessed with Western blotting using the anti-nNOS antibody. Compared with control (normal Ringer solution), nNOS protein levels were time-dependently (0.5, 1, 2, and 5 hrs) increased on the addition of furosemide (loop diureticus). NO release from the NE-MD cells was measured in the presence of 1 mM L-arginine by using the NO sensitive electrode. NO production levels were also time-dependently (2 and 5 hrs) increased on the addition of furosemide, which was dose-dependently (10-50 µM) inhibited by 7-nitroindazole (nNOS specific inhibitor). Similar changes were seen in the NO release when extracellular Cl− concentration was decreased (1/10), but NOT by Na+. Furosemide-induced NO generation was completely cancelled when the NE-MD cells were co-incubated with BAPTA-AM (a Ca2+ chelator). These results suggest that nNOS expression and NO release in the NE-MD cells is inversely regulated by extracellular Cl− concentration, but NOT by Na+ concentration, and that these subcellular mechanisms are sensitive to intracellular Ca2+ concentration. [Jpn J Physiol 55 Suppl:S77 (2005)]
