Isoform selectivity of 3-125I-iodo-alpha-methyl-L-tyrosine membrane transport in human L-type amino acid transporters.

3-(123)I-Iodo-alpha-methyl-L-tyrosine ((123)I-IMT) has been developed for SPECT of amino acid transport imaging. We examined the isoform selectivity of (125)I-IMT transport of the 2 human L-type amino acid transporters, hLAT1 and hLAT2, with human 4F2hc-coexpressed Xenopus laevis oocytes. METHODS: An uptake study of (125)I-IMT was performed using transporter-expressed X. laevis oocytes. Oocytes were injected with 17.6 ng of hLAT1 or hLAT2 complementary RNA (cRNA) and 7.4 ng of h4F2hc cRNA in a molar ratio of 1:1. Two days after injection, the uptake of (125)I-IMT was measured in the Na(+)-free uptake solution containing 18.5 kBq of noncarrier-added (125)I-IMT. After incubation for 30 min at room temperature, radioactivity of the oocytes was determined. RESULTS: Of the 2 hLAT isoforms and h4F2hc-coexpressed X. laevis oocytes, (125)I-IMT uptake via hLAT1 was 5.95-fold higher than that via hLAT2 (P < 0.005). CONCLUSION: (125)I-IMT transport was hLAT1 selective. Investigations on the isoform selectivity of (125)I-IMT transport with other transporters are anticipated.