Kinetic characteristics of folate binding to rat renal brush border membrane in chronic alcoholism.

The binding of folic acid to the plasma membrane is an important event for its reabsorption and conservation by renal epithelium. We studied [3H] folic acid binding to the renal cortical brush border membrane vesicles (BBMV) in rats after 12 weeks of chronic ethanol ingestion. Our results demonstrated that after chronic ethanol intake, the binding of folic acid to the membrane vesicles: (1) was decreased by a mechanism that decreased B(max) without affecting K(d), (2) was insensitive to Na+ ions in the medium (3) behaved differently to divalent cations in the medium in contrast to control group. However under such conditions there was no significant effect of ethanol on pH optimum of the process. Binding was reduced at pH less than 6 but there was no effect of ethanol on binding in pH range from 6 to 8. Increasing the osmolarity at pH 5.5 had no effect on the binding of folate to BBMV, thus confirming that the observed changes in B(max) values were due to site-specific binding in the two groups. Moreover, ethanol does not impart its effect on involvement of sulfhydryl group at the binding site of folate transport system. These findings highlight the possible mechanism of perturbed renal conservation of folate during chronic alcoholism.