Glutamate is transported across the rat blood-brain barrier by a sodium-independent system.
Transport of L-glutamate from blood to brain in equithesin-anesthetized rats was examined using in situ brain perfusion combined with multiple-time/graphical analysis. In situ perfusion allowed precise control of the composition of the perfusate, which was necessary for a detailed investigation of glutamate transport, while multiple time/graphical analysis permitted evaluation of the rapidly reversible volume and the period when the influx was unidirectional. Glutamate had no reversible volume and efflux from brain occurred after 30 s of perfusion. The in situ transfer coefficient (Kin) ranged from 0.74 +/- 0.07 mul/s per g in parietal cortex to 0.44 +/- 0.07 mul/s per g in hippocampus. L-Glutamate uptake was unaffected by removal of sodium from the perfusate, reduced by 5 mM L-glutamate, L-homocysteate, L-aspartate, plasma and 0.1 mM L-glutamate, while L-cystine did not reduce its uptake. These results suggest that the transport system for glutamate is saturated mainly by L-glutamate at physiological conditions and that it is not the sodium-independent x-C system since glutamate transport was not reduced by L-cystine except in hippocampus and that it was responsive to L-aspartate.
Benrabh
H
H
INSERM U26, Hopital F. Widal, Paris, France.
Lefauconnier
J M
JM
D018528:ATP-Binding Cassette Transporters / Q000502:physiology; D027322:Amino Acid Transport System X-AG; D000818:Animals; D001224:Aspartic Acid / Q000494:pharmacology; D001692:Biological Transport / Q000502:physiology; D001812:Blood-Brain Barrier / Q000187:drug effects / Q000502:physiology*; D003553:Cystine / Q000378:metabolism; D018698:Glutamic Acid / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D010477:Perfusion; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000378:metabolism*; D013997:Time Factors
D018528:ATP-Binding Cassette Transporters; D027322:Amino Acid Transport System X-AG; D001224:Aspartic Acid; D018698:Glutamic Acid; D003553:Cystine; D012964:Sodium