L-arginine transport mechanism in the pigmented rabbit conjunctiva

Purpose. To characterize L-arginine (L-Arg) transport in the pigmented rabbit conjunctiva. Method. The excised pigmented rabbit conjunctiva was mounted in the modified Ussing chamber for measurement of short-circuit current (Isc) and ³H-L-Arg flux. Results. L-Arg when added to the mucosal side at 37°C led to 0.32-2.65 μA/cm² increase in Isc. L-Arg transport at 0.1 mM in the mucosal to the serosal (M->S) direction was approximately 16-times faster than that in the opposite direction. The evidence for the carrier-mediated M->S transport of L-Arg includes: (1) temperature dependence and saturablility, (2) Na⁺-dependency and ouabain sensitivity, and (3) reduction in the apparent permeability by 84 ± 2% by excess unlabeled L-Arg (1 mM). Hill analysis of L-Arg transport at 0.1 mM in the presence of varying Na⁺ concentrations in the mucosal bathing fluid yielded a Hill coefficient of 0.93. L-Arg transport was inhibited by L-Lys, L-Orn, L-Phe, L-Leu, and nitric oxide synthase (NOS) inhibitors such as N^G-nitro-L-arginine, N^G-nitro-L-arginine methyl ester, and N^G-monomethyl-L-arginine, but not by L-Glu and Gly. Conclusion. L-Arg transport, which exhibits 1: 1 stoichiometry with Na⁺ and seems to be shared by basic amino acids, large neutral amino acids, and NOS inhibitors, is probably mediated by the system B^0,+.