Cl−HCO3 exchange in rat renal basolateral membrane vesicles |
| |
Authors: | Steven M Grassl Peter D Holohan Charles R Ross |
| |
Abstract: | Pathways for HCO3− transport across the basolateral membrane were investigated using membrane vesicles isolated from rat renal cortex. The presence of Cl−---HCO3− exchange was assessed directly by 36Cl− tracer flux measurements and indirectly by determinants of acridine orange absorbance changes. Under 10% CO2/90% N2 the imposition of an outwardly directed HCO3− concentration gradient (pHo 6/pHi 7.5) stimulated Cl− uptake compared to Cl− uptake under 100% N2 in the presence of a pH gradient alone. Mediated exchange of Cl− for HCO3 was suggested by the HCO3− gradient-induced concentrative accumulation of intravesicular Cl−. Maneuvers designed to offset the development of ion-gradient-induced diffusion potentials had no significant effect on the magnitude of HCO3− gradient-driven Cl− uptake further suggesting chemical as opposed to electrical Cl−HCO3− exchange coupling. Although basolateral membrane vesicle Cl− uptake was observed to be voltage sensitive, the DIDS insensitivity of the Cl conductive pathway served to distinguish this mode of Cl− translocation from HCO3 gradient-driven Cl− uptake. No evidence for cotransport was obtained. As determined by acridine orange absorbance measurements in the presence of an imposed pH gradient (pHo 7.5/pHi 6), a HCO3− dependent increase in the rate of intravesicular alkalinization was observed in response to an outwardly directed Cl− concentration gradient. The basolateral membrane vesicle origin of the observed Cl−−HCO3− exchange activity was verified by experiments performed with purified brush-border membrane vesicles. In contrast to our previous observations of the effect of Cl− on HCO3− gradient-driven Na+ uptake suggesting a basolateral membrane Na+−HCO3− for Cl− exchange mechanism, no effect of Na+ on Cl−HCO3− exchange was observed in the present study. |
| |
Keywords: | Chloride bicarbonate ion exchange Bicarbonate ion transport Kidney tubule Basolateral membrane vesicle (Rat kidney) |
本文献已被 ScienceDirect 等数据库收录! |