Previous work on snake proximal-proximal (ppt) and distal-proximal (dpt) tubules with oil-filled lumens in HEPES (25 mM)-buffered medium suggested that basolateral [Na+] could affect pHi. We now evaluated regulation of pHi, measured with fluorescent dye BCECF, in both absence and presence of HCO3-. Resting pHi was 7.1-7.2 in ppt and dpt in HEPES-buffered medium and in ppt in HEPES (20 mM)/HCO3- (5 mM)-buffered medium, but -7.3 in dpt in HEPES/HCO3- buffer. pHi increased to 7.6-7.7 with addition of NH4Cl (20 mM) and then decreased to 6.9-7.0 with its removal in ppt and dpt in both buffers. Control rate of recovery (dpHi/dt) from acid level was 3.9 X 10-3 pH U/s, except for dpt in HEPES/HCO3- buffer where it was 5.2 X 10-3 pH U/s. dpHi/dt was reduced by Na+ removal in dpt in HEPES buffer but was not affected by Na+ removal in ppt or dpt in HEPES/HCO3- buffer. It was not affected by Cl-, or both Na+ and Cl- removal or the presence of Ba2+ (5 mM) or high K+ (75 mM) in either HEPES or HEPES/HCO3- buffer. Anion exchange inhibitor DIDS (100 μM) reduced dpHi/dt only in dpt and only in HEPES/HCO3- buffer. Na+/H+ exchange inhibitor EIPA (100 μM) reduced dpHi/dt slightly but significantly in dpt, but not ppt in both HEPES and HEPES/HCO3- buffers. These data do not clearly support basolateral regulation of pHi by the most common Na+/H+, Na+-dependent and Na+-independent Cl-/HCO3- exchangers, or Na+-HCO3-CO32- cotransporter.
|Original language||English (US)|
|State||Published - Mar 20 1998|