Effects of divalent cations and pH on amiloride-sensitive Na+ fluxes into luminal membrane vesicles from pars recta of rabbit proximal tubule

The Pharmacological Profile of Brain Liver Intestine Na+ Channel: Inhibition by Diarylamidines and Activation by Fenamates

“…Those currents include a Na ϩ -selective channel from rabbit proximal tubules (Gögelein and Greger, 1986;Jacobsen et al, 1988) that is sensitive to Ca 2ϩ (Blokkebak-Poulsen et al, 1991) and a Na ϩ channel in LLC-PK1 cells (Raychowdhury et al, 2004), a cell line with proximal tubule characteristics derived from pig kidney. Furthermore, several studies describe an amilorideinsensitive and thus ENaC-independent pathway for Na ϩ entry in epithelial cells of various organs, such as lung (Shlyonsky et al, 2005), colon (Inagaki et al, 2004), and esophagus (Awayda et al, 2004).…”

Effects of [Ca2+]i and pH on epithelial Na+ channel activity of cultured mouse cortical collecting ducts

“…ENaC activity is regulated by a variety of hormones, e.g. aldosterone and antidiuretic hormone (ADH), as well as by the luminal contents (Blokkebak-Poulsen et al, 1991;Palmer and Frindt, 1987). A millimolar concentration of Ca 2+ intravesicularly was found to block the amiloride-sensitive 22 …”

“…This inhibitory effect of Ca 2+ was dependent on pH (Blokkebak-Poulsen et al, 1991) and probably due to increase of [Ca 2+ ] i (Chase and AlAwqati, 1981 ] i elevation in tubule cells is mediated by either Ca 2+ release from internal store or Ca 2+ uptake across the apical membrane via different calcium channels Leclerc et al, 2004) (Brunette and Leclerc, 2002), and is proportional to the outward Na + gradient (Chase and Al-Awqati, 1981). Ca 2+ as an important second messenger, has been implicated to inhibit ENaCs (Wang and Chan, 2000).…”

“…Trans epithelial Na + transport rate is increased by intracellular alkalization but decreased by intracellular acidosis (Blokkebak-Poulsen et al, 1991;Harvey et al, 1988;. Controversially, in toad bladder, acidification of the cytoplasm can stimulate Na + transport (Garty et al, 1987;Leaf et al, 1964).…”

“…However, amiloride-sensitive Na + fluxes in toad urinary bladder are not affected by changes in pH i over the range of pH 7-8, suggesting a indirect regulation mechanism by pH i (Garty and Asher, 1985). It is postulated that pH exerts its effect by altering the inhibitory effect of Ca 2+ on ENaC (Blokkebak-Poulsen et al, 1991). Therefore, in this study, inside-out recording were employed to elucidate the direct effects of [Ca 2+ ] i and pH i on ENaC activity of cultured mouse cortical collecting ducts.…”