Transcellular transport of domoic acid across intestinal Caco-2 cell monolayers

The intestinal absorption mechanism of domoic acid (DA) was investigated using Caco-2 cells. DA is a tricarboxylic amino acid that contains a glutamic acid moiety, and causes deficits in short-term memory by binding to glutamate receptors as an agonist of glutamic acid. Caco-2 cell monolayers cultured on permeable membranes were incubated with 100 μM DA on either the apical or basolateral side, and the transcellular transport of DA was measured. The transcellular transport of DA from the apical to basolateral side was about twofold that in the opposite direction. The transcellular transport of DA from the apical side was optimal at a neutral pH, and was temperature- and Cl−-dependent, but was Na+-independent. Coincubation of DA with 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid (DIDS), an anion exchange inhibitor, significantly decreased the apical-to-basolateral transport of DA by 48%, and coincubation with probenecid (a non-specific anion transport inhibitor) significantly decreased the transport of DA by 31%. In contrast, coincubation with glutamic acid, succinic acid (a dicarboxylic acid), or citric acid (a tricarboxylic acid) did not decrease the transport of DA. These results suggest that the apical-to-basolateral transport of DA across the Caco-2 cell monolayers is mediated by DIDS-sensitive anion transporters.