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It limits how far mouse OCT1 results can be read as human ones; it is not itself a human tissue measurement.\nexposure: Metformin and thiamine uptake kinetics; transmembrane-helix substitutions\nevidence_span: {\"source_cache\": \"artifacts/metformin-research/33037045.abstract.txt\", \"locator\": \"Indexed abstract; zero-based, end-exclusive Unicode character offsets\", \"file_sha256\": \"861e39b20a78d5d85a01c5de0febda8bf1c400de4fa8ef1e6944707521604c67\", \"start_char\": 0, \"end_char\": 2296, \"text_sha256\": \"861e39b20a78d5d85a01c5de0febda8bf1c400de4fa8ef1e6944707521604c67\"}\n[metformin-p33037045] Differences in Metformin and Thiamine Uptake between Human and Mouse Organic Cation Transporter 1: Structural Determinants and Potential Consequences for Intrahepatic Concentrations. 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