Sodium-dependent inhibition of amino acid and dipeptide transport by harmaline in monkey small intestine

The effect of harmaline on amino acid and dipeptide uptake was studied in the monkey. Harmaline inhibited both the systems. Preincubation of the tissue with 4 mmole/1 harmaline for 10 min was necessary for maximal inhibition. The uptake of glycyl-L-leucine- (14C) and (14C)-glycyl-l-leucine was inhibited to the same extent. The uptake of glycyl-L-proline, a dipeptide which was presumably taken up intact by the mucosal cells, was also inhibited. Total replacement of sodium in the medium reduced the uptake of both glycyl-L-leucine and glycyl-L-proline. But the uptake of these dipeptides was not inhibited by harmaline in the absence of sodium. However, the sodium-independent uptake of glycyl-L-leucine and glycyl-L-proline was also inhibited by other dipeptides