Article ID Journal Published Year Pages File Type
10798281 Biochimica et Biophysica Acta (BBA) - Biomembranes 2005 6 Pages PDF
Abstract
hCAT-3 (human cationic amino acid transporter type three) was investigated with both the two-electrode voltage clamp method and tracer experiments. Oocytes expressing hCAT-3 displayed less negative membrane potentials and larger voltage-dependent currents than native or water-injected oocytes did. Ion substitution experiments in hCAT-3-expressing oocytes revealed a large conductance for Na+ and K+. In the presence of l-Arg, voltage-dependent inward and outward currents were observed. At symmetrical (inside/outside) concentrations of l-Arg, the conductance of the transporter increased monoexponentially with the l-Arg concentrations; the calculated Vmax and KM values amounted to 8.3 μS and 0.36 mM, respectively. The time constants of influx and efflux of [3H]l-Arg, at symmetrically inside/outside l-Arg concentrations (1 mM), amounted to 79 and 77 min, respectively. The flux data and electrophysiological experiments suggest that the transport of l-Arg through hCAT-3 is symmetric, when the steady state of l-Arg flux has been reached. It is concluded that hCAT-3 is a passive transport system that conducts monovalent cations including l-Arg. The particular role of hCAT-3 in the diverse tissues remains to be elucidated.
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Life Sciences Biochemistry, Genetics and Molecular Biology Biochemistry
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