Evidence for a lactate-anion exchanger in the rat jejunal basolateral membrane

Abstract Background/Aims: The mechanism by which lactate, absorbed from the intestinal lumen or generated within the epithelium, crosses the basolateral membrane of the enterocyte and enters the bloodstream has not previously been characterized in detail. Methods: l-lactate uptake into and efflux from isolated jejunal basolateral membrane vesicles was investigated at room temperature using rapid filtration techniques. Results: Furosemide sensitive uptake of l-lactate was unaffected by cis sodium or proton gradients but could be stimulated by a trans gradient of bicarbonate and chloride. Kinetic analysis showed uptake to consist of a saturable component with a Michaelis constant ( K m ) of 3.2 mmol/L and a maximum velocity (V max ) of 67 pmol·mg protein −1 · s −1 and a nonsaturable α-4-hydroxy-cinnamic acid insensitive component. Pyruvate, butyrate, acetate, valerate, and proprionate competitively inhibited lactate uptake into the vesicles. Efflux of lactate from preloaded vesicles was furosemide sensitive and accelerated by a trans bicarbonate gradient as well as by 10 mmol/L acetate, butyrate, and pyruvate. Conclusions: It is concluded that there is a short chain-fatty acid carrier system in the intestinal basolateral membrane, which operates as an anion exchanger.