OLEIC-ACID INHIBITION OF NA+/D-GLUCOSE TRANSPORT IN ISOLATED RENAL BRUSH-BORDER MEMBRANES - ROLE OF LIPID PHYSICAL PARAMETERS AND TRANS NA+-INHIBITION

Inhibition of Na+/D-glucose transport by oleic acid was investigated in renal brush-border membrane vesicles (BBMV). Lipid physical parameters were determined by spectrofluorometry. cis-Unsaturated C-16-C22 long-chain fatty acids (LCFA) as oleic acid reduced nonzero limiting anisotropy r(infinity) with DPH and 12-AS as probes and decreased rotational correlation time phi of 12-AS. At 8 s and 15 s Na+/D-glucose transport was competitively inhibited. A positive correlation existed between decrease in r(infinity) (acyl chain order) or decrease in rotational correlation time phi (= increase in 'fluidity') and inhibition of Na+/D-glucose transport. Except elaidic acid trans unsaturated and saturated LCFA had no effect on fluorescence anisotropy and Na+/D-glucose transport. Per cent transport inhibition was unaffected by 0 voltage clamping and by FCCP. K(i) for trans Na+-inhibition of D-glucose transport was 29 mmol/l. Na+-transport was stimulated by oleic acid, exceeding the K(i) value for trans Na+ inhibition. Conclusion: oleic acid inhibits Na+/D-glucose transport by a decrease in lipid acyl chain order and an increase in 'fluidity', by trans Na+-inhibition and presumably by a third unknown mechanism.