Abstract
The properties of carnosine (Car) and glycylglycine (Gly-Gly), transported across the mucosal border, were studied in isolated guinea pig everted ileum. The initial influxes of both dipeptides could be described by single Michaelis-Menten kinetics, having a nearly equal value of maximum influx. Mutual inhibition studies showed that the inhibition observed between Car and Gly-Gly was fully competitive, indicating that both Car and Gly-Gly share a common carrier. Although carrier-mediated influxes of the dipeptides were independent of Na+, the addition of the dipeptides into the mucosal solution evoked sudden and sustained increments of mucosal negativity. The changes in short-circuit current (ΔIsc) evoked by the peptides increased as the Na+ concentration in the solution was increased, although both dipeptides evoked small increases in Isc, even in the absence of Na+ In spite of these common properties of transport and transport-related electrical phenomena, it was seen that the maximum change in transmural potential difference (ΔPDt max) evoked by Car was about half that of Gly-Gly. Such a discrepancy between coincident Jmax values and values of ΔPDt max suggests that the mechanism of induction of ionic flow is different for these two dipeptides.
