Possible existence of Na(+)-coupled amino acid transport in the pigmented rabbit conjunctiva

The objective of the present study was to determine whether Na(+)-amino acid cotransport contributed to the short-circuit current (ISC) in the isolated pigmented rabbit conjunctiva. Glycine, L-arginine, D-arginine, and L-glutamic acid were the amino acids tested, and bioelectric measurements were made in the Using chamber. The ISC was increased from 4% (L-glutamic acid) to 44% (L-arginine). The EC50 was 0.35 mM for glycine, 0.06 mM for L-arginine, 0.16 mM for D-arginine, and 1 mM for L-glutamic acid. No elevation in ISC was seen in the absence of Na+ in the mucosal bathing fluid. The above findings are consistent with the possible existence of a Na(+)-amino acid cotransport process on the apical side of the pigmented rabbit conjunctiva.