BASOLATERAL CL HCO3 EXCHANGE IN RAT JEJUNUM - THE EFFECT OF SODIUM/

Basolateral membrane vesicles isolated from rat jejunum were used to c haracterize a Cl/HCO3 exchange mechanism previously evidenced. Cl upta ke experiments provided no evidence for Cl/OH countertransport, confir ming anyhow the presence of Cl/HCO3 antiport, which was inhibited by 2 mm furosemide and unaffected by 2 mm amiloride. An outwardly directed Na gradient stimulated Cl uptake and this effect was increased if Na was present at both vesicle surfaces. To investigate the mechanism of coupling between Na and the transport protein, we performed Na uptake experiments. Na uptake was unaffected by cis-bicarbonate and trans-Cl gradients; the reversal of anion gradients was still ineffective. Simi lar results were obtained when a pH difference across the membrane ves icles was imposed. This study seems to suggest that Na is not transpor ted by the Cl/HCO3 exchanger and that another mode of Na dependence mu st be taken into account.