Circadian variation in the uptake of tryptophan by cortical synaptosomes of the rat brain.
The kinetics of the high affinity uptake system for L-tryptophan (L-Try) have been measured over 24 hr in cortical synaptosome preparations of rat brain. Both the Km and Vmax of the uptake process showed a statistically significant 24 hr variation. The highest Km value, 6.71 X 10(-5) M, was measured at the beginning of the light phase and the lowest value, 4.23 X 10(-5) M, 6 hr into the dark phase. Vmax was highest at the end of the dark phase (10.43 nmol/mg/5 min) and lowest (4.80 nmol/mg/5 min) 3 hr into the dark phase. In contrast, there was no variation over 24 hr in the Vmax/Km ratio. These results suggest that the high affinity uptake process serves to ensure a constant rate of L-tryptophan entry into the neuron in the face of circadian or ultradian variations in extracellular concentration of tryptophan.
Loizou
G
G
Pharmacology Group, School of Pharmacy and Pharmacology, University of Bath, U.K.
Redfern
P H
PH
D000818:Animals; D001692:Biological Transport; D002540:Cerebral Cortex / Q000378:metabolism*; D002940:Circadian Rhythm; D003624:Darkness; D007700:Kinetics; D008027:Light; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D013574:Synaptosomes / Q000378:metabolism*; D014364:Tryptophan / Q000378:metabolism*
D014364:Tryptophan