In rabbit cortical collecting duct, Cl- self exchange accounts for most of the transepithelial Cl- tracer rate coefficient, K(Cl) (nm/s); a small fraction is effected by Cl--HCO3- exchange and Cl- diffusion. We previously reported that changing from a CO2-free N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES) bath to a 5% CO2-25 mM HCO3- bath stimulates Cl- self exchange. Here, we examine in further detail the individual components of the CO2-HCO3- system that stimulate K(Cl). Addition of 0.5% CO2 to a HEPES bath (final pH = 7.24) stimulated K(Cl) by 70 ± 19 nm/s, a ΔK(Cl) comparable to that induced by 1% CO2 (pH 7.12), 6% CO2 (pH 6.6), or 6% CO2-25 mM HCO3- (pH 7.4). The roles of intracellular pH (pH(i)) and HCO3- concentration were examined by clamping pH(i) using high K+ and nigericin. Increasing pH(i) from 6.9 to 7.6 in solutions without exogenous CO2 or HCO3- increased K(Cl) by 71 ± 17 nm/s. These results suggest that pH(i) might regulate anion exchange. However, during such a pH(i)-shift experiment, metabolically derived CO2 produces a concomitant change in intracellular HCO3- concentration ([HCO3-](i)). To determine whether an increase in [HCO3-](i) could stimulate Cl- self exchange, we replaced HEPES with 6% CO2-5 mM HCO3- isohydrically (pH(i) clamped at 6.9). With this increase in [HCO3-](i) at constant pH(i), K(Cl) increased by 51 ± 10 nm/s. These maneuvers had negligible effects on Cl- diffusion and Cl--HCO3- exchange. These experiments demonstrate that increases in cell [HCO3-] (or perhaps CO2) can stimulate transepithelial anion exchange. Although pH(i) may also have an effect on the anion exchange process, under the present conditions, the HCO3- effect seems to be more potent and is evident at low concentrations of HCO3- and CO2.
|Original language||English (US)|
|Journal||American Journal of Physiology - Cell Physiology|
|State||Published - Jan 1 1989|
ASJC Scopus subject areas
- Cell Biology