title: Na(+)-dependent transport of taurine is found only on the abluminal membrane of the blood-brain barrier.
abstract: Luminal and abluminal plasma membranes were isolated from bovine brain microvessels and used to identify and characterize Na(+)-dependent and facilitative taurine transport. The calculated transmembrane potential was -59 mV at time 0; external Na(+) (or choline under putative zero-trans conditions) was 126 mM (T=25 °C). The apparent affinity constants of the taurine transporters were determined over a range of taurine concentrations from 0.24 μM to 11.4 μM. Abluminal membranes had both Na(+)-dependent taurine transport as well as facilitative transport while luminal membranes only had facilitative transport. The apparent K(m) for facilitative and Na(+)-dependent taurine transport were 0.06±0.02 μM and 0.7±0.1 μM, respectively. The Na(+)-dependent transport of taurine was voltage dependent over the range of voltages studied (-25 to -101 mV). The transport was over 5 times greater at -101 mV compared to when V(m) was -25 mV. The sensitivity to external osmolality of Na(+)-dependent transport was studied over a range of osmolalities (229 to 398 mOsm/kg H(2)O) using mannitol as the osmotic agent to adjust the osmolality. For these experiments the concentration of Na(+) was maintained constant at 50mM, and the calculated transmembrane potential was -59 mV. The Na(+)-dependent transport system was sensitive to osmolality with the greatest rate observed at 229 mOsm/kg H(2)O.
authors: Department of Physiology & Biophysics, The Chicago Medical School, Rosalind Franklin University of Medicine and Science, 3333 Green Bay Road, North Chicago, IL 60064-3095 USA. Hector.Rasgado@rosalindfranklin.edu
authors: Hector
authors: H
authors: Rasgado-Flores
authors: Ashwini
authors: A
authors: Mokashi
authors: Richard A
authors: RA
authors: Hawkins
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001693:Biological Transport, Active; D001812:Blood-Brain Barrier / Q000166:cytology* / Q000502:physiology*; D002199:Capillary Permeability / Q000502:physiology; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism*; D009994:Osmolar Concentration; D012964:Sodium / Q000378:metabolism*; D013654:Taurine / Q000378:metabolism*; D013997:Time Factors; D014316:Tritium / Q000378:metabolism
chemical_list: D014316:Tritium; D013654:Taurine; D012964:Sodium