The transport mechanism of aminoβ-lactam antibiotics across in vitro rat ileum was examined using the electrophysiological technique in comparison with that of dipeptides. The changes in the transmural potential difference (PDt) induced by a series of aminoβ-lactam antibiotics were correlated with the absorption percentage of these antibiotics from the in situ rat intestinal loops. On the contrary, β-lactam antibiotics without a-amino group such as dicloxacillin, methicillin and cefazolin did not induce such a stable change of PDV The changes in PDt induced by cyclacillin (ACPC), cefadroxil (CDX) and glycylgly-cine (Gly-Gly) became saturable when the concentration of the substances increased. The half saturation concentration for ACPC, CDX, and Gly-Gly estimated from the changes in PDt was nearly identical with that determined from influx of the substrates in the everted intestinal sacs. The mutual inhibition between amino-β-lactam antibiotics and Gly-Gly was observed in their induced PDts. The changes in PDt induced by aminoβ-lactam antibiotics were independent of those of glucose, glycine, and cefazolin. By the removal of Na+ from the mucosal solution, the PDt decreased one-fifth of the PDt induced in the presence of Na+. These results suggest that aminoβ-lactam antibiotic-induced PDt relates to the Na+ ion fluxes as reported for dipeptides.
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