Basolateral Cl −/HCO −3 exchange in rat jejunum: Evidence from H 14CO −3 uptake in membrane vesicles

Abstract

Bicarbonate transport across basolateral membrane vesicles from rat jejunal enterocyte was studied at 28°C and pH 8.2. These experimental conditions make possible the determination of [ 14C]bicarbonate uptake. Inward gradients of Na +, K +, and Li + did not stimulate HCO − 3 uptake, suggesting that a cotransport mechanism with these cations does not occur. On the contrary a countertransport of bicarbonate driven by a Cl − gradient was evidenced. The ability of other inorganic anions to exchange with HCO − 3 was examined and results indicate that Cl − can be substituted by NO − 3, Br − and SCN −. The Cl −-dependent HCO − 3 uptake was strongly inhibited by SITS and DIDS, whereas acetazolamide was ineffective: thus transfer of labelled CO 2 is eliminated as a possible mode of HCO − 3 permeation. HCO − 3 uptake was also affected by the presence of superimposed membrane potentials, suggesting that a HCO − 3 conductive pathway is present in the jejunal basolateral membrane. These results show that there are no fundamental differences between data obtained performing H 14CO − 3 and 36Cl − (previously reported) uptake experiments.