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A MODEL OF HIGH AFFINITY GLUTAMIC ACID TRANSPORT BY CORTICAL SYNAPTOSOMES FROM THE LONG‐EVANS RAT
Author(s) -
Wheeler D. D.,
Hollingsworth R. G.
Publication year - 1978
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1978.tb10461.x
Subject(s) - sodium , chemistry , glutamic acid , membrane , coupling (piping) , biophysics , biochemistry , amino acid , organic chemistry , biology , materials science , metallurgy
— The initial velocity of uptake of L‐glutamic acid by cortical synaptosomes from the Long‐Evans rat has been measured as a function of sodium and glutamic acid concentration. These data were then fitted to the rate equation from each of several possible models, and the model giving minimum error identified. The major predictions from the best fit model are as follows: (1) The order of combination with the carrier should be sodium, sodium, glutamic acid. (2) Uptake should be 100% dependent on the presence of sodium in the incubation medium. (3) At a finite concentration of sodium, V mx should be independent of the sodium concentration, which implies that translocation of the carrier across the membrane is independent of the sodium concentration. (4) Lineweaver‐Burk plots should be linear with slopes depending on the sodium Concentration. (5) There should be co‐transport of two sodium ions with each glutamic acid molecule. (6) The dependence of K t , on the sodium concentration should have the following form: K t = A/[Na] 2 + 8/[Na] + C , where A, B , and C are constants. The results differ substantially from those previously reported for Sprague‐Dawley rats. K t , is 2–5 times less than that for Sprfague‐Dawley rats, and the relation of sodium to K t , is basically different. We also find a coupling ratio of two, whereas previous studies found a coupling ratio of one. Thus the results raise the possibility that there are fundamental differences between Sprague‐Dawley and Long‐Evans rats with regard to the mechanism by which sodium participates in amino acid transport.