Ionic dependence of glycylsarcosine uptake by isolated chicken enterocytes

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Abstract
Dipeptide transport was studied in chicken enterocytes and its properties compared with those of Na+‐dependent sugar transport. Results showed that 1) isolated cells were capable of accumulating glycylsarcosine (Gly‐Sar) against a concentration gradient (2.5‐ to 3.0‐fold accumulation). This uptake was maximal at pH 6.0, and it was inhibited by Na+‐free medium and by ouabaine; 2) uptake of Gly‐Sar was not affected by methionine and was competitively inhibited by carnosine, with a Ki of 12 mM; 3) the protonophore FCCP inhibited both Gly‐Sar and 3‐oxy‐methyl‐D‐glucose (3‐OMG) uptake by the cells; 4) amiloride, a well‐known inhibitor of the Na+/H+ exchanger system stimulated 3‐OMG uptake and inhibited Gly‐Sar uptake, its effects being greater at pH 7.4; 5) and monensine prevents the effects of amiloride on both sugar and dipeptide uptake. In summary, Gly‐Sar uptake depends on extracellular Na+ in an indirect manner via its effect on H+ efflux, and it appears to be dependent on an inward H+ gradient.