Previous data indicated that basolateral regulation of proximal tubule pHi differed between avian nephron types in the absence of HCO3-. Therefore, we evaluated regulation of pHi, measured with fluorescent dye BCECF, in chicken loopless reptilian-type (lrt) and long-looped mammalian-type (l-lmt) nephrons in HEPES (20 mM)/HCO3- (5 mM)-buffered medium. In both nephron types, proximal pHi was ∼7.1 under control circumstances (pH 7.4; 37°C) and increased to ∼7.4 with addition of NH4Cl (20 mM) and then decreased to ∼6.8 with its removal. Intrinsic buffering capacity was 88-91 mM H+/pH U, basolateral NH3 flux was 3.2-3.6 nmol cm-2 s-1, and basolateral NH3 permeability was 6.4-7.4 X 10-3 cm s-1. Also, in both nephron types control rate of recovery (dpHi/dt) from acid level (5.2-6.6 X 10-3 pH U/s) and resting pHi were reduced by Na+ removal. Na+/H+ exchange inhibitor EIPA (100 μM) and anion exchange inhibitor DIDS (100 μM) decreased dpHi/dt in proximal tubules of l-lmt but not lrt nephrons. Removal of Cl-, addition of Ba2+ (5 mM), or presence of high K+ (75 mM) had no effect on dpHi/dt in either nephron type. In l-lmt nephrons, these data support presence of a basolateral Na+/H+ exchanger and possibly a Na+-HCO3--CO32- cotransporter, but other acid/base transporters must account for regulation in lrt nephrons.
|Original language||English (US)|
|State||Published - Mar 20 1998|
ASJC Scopus subject areas
- Molecular Biology