title: Quantifying the relative contributions of different solute carriers to aggregate substrate transport.
abstract: Determining the contributions of different transporter species to overall cellular transport is fundamental for understanding the physiological regulation of solutes. We calculated the relative activities of Solute Carrier (SLC) transporters using the Michaelis-Menten equation and global fitting to estimate the normalized maximum transport rate for each transporter (Vmax). Data input were the normalized measured uptake of the essential neutral amino acid (AA) L-leucine (Leu) from concentration-dependence assays performed using Xenopus laevis oocytes. Our methodology was verified by calculating Leu and L-phenylalanine (Phe) data in the presence of competitive substrates and/or inhibitors. Among 9 potentially expressed endogenous X. laevis oocyte Leu transporter species, activities of only the uniporters SLC43A2/LAT4 (and/or SLC43A1/LAT3) and the sodium symporter SLC6A19/B0AT1 were required to account for total uptake. Furthermore, Leu and Phe uptake by heterologously expressed human SLC6A14/ATB0,+and SLC43A2/LAT4 was accurately calculated. This versatile systems biology approach is useful for analyses where the kinetics of each active protein species can be represented by the Hill equation. Furthermore, its applicable even in the absence of protein expression data. It could potentially be applied, for example, to quantify drug transporter activities in target cells to improve specificity.
authors.affiliation: The Interface Group, Institute of Physiology, University of Zurich, Switzerland.|Epithelial Transport Group, Institute of Physiology, University of Zurich, Switzerland.
authors.forename: Mehdi
authors.initials: M
authors.lastname: Taslimifar
authors.affiliation: Epithelial Transport Group, Institute of Physiology, University of Zurich, Switzerland.|Zurich Center for Integrative Human Physiology, University of Zurich, Switzerland.
authors.forename: Lalita
authors.initials: L
authors.lastname: Oparija
authors.affiliation: Epithelial Transport Group, Institute of Physiology, University of Zurich, Switzerland.|Zurich Center for Integrative Human Physiology, University of Zurich, Switzerland.|National Center of Competence in Research, Kidney CH, Switzerland.
authors.forename: Francois
authors.initials: F
authors.lastname: Verrey
authors.affiliation: The Interface Group, Institute of Physiology, University of Zurich, Switzerland.|Zurich Center for Integrative Human Physiology, University of Zurich, Switzerland.|National Center of Competence in Research, Kidney CH, Switzerland.
authors.forename: Vartan
authors.initials: V
authors.lastname: Kurtcuoglu
authors.affiliation: The Interface Group, Institute of Physiology, University of Zurich, Switzerland.|National Center of Competence in Research, Kidney CH, Switzerland.
authors.forename: Ufuk
authors.initials: U
authors.lastname: Olgac
authors.affiliation: Epithelial Transport Group, Institute of Physiology, University of Zurich, Switzerland.
authors.forename: Victoria
authors.initials: V
authors.lastname: Makrides
mesh_terms: D000818:Animals; D001692:Biological Transport; D006801:Humans; D007700:Kinetics; D007930:Leucine / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000378:metabolism*; D008954:Models, Biological; D009865:Oocytes / Q000378:metabolism; D010649:Phenylalanine / Q000378:metabolism; D013379:Substrate Specificity; D014982:Xenopus laevis / Q000378:metabolism
chemical_list: D026901:Membrane Transport Proteins; D010649:Phenylalanine; D007930:Leucine