A Kinetic Analysis of Sodium Dependent Glutamic Acid Transport in Peripheral Nerve

Abstract

—The kinetics of sodium dependent glutamic acid transport have been studied in desheathed frog sciatic nerve. Initial velocities have been measured as a function of both glulamic acid and sodium concentration. Lineweaver–Burk plots are constructed from these data, and the kinetic constants describing uptake are estimated. Vmax is unaffected by sodium concentration, which implies that translocation is not directly affected by sodium. K1 is sodium dependent, which implies that sodium affects the affinity of the carrier for glutamic acid. Reciprocal plots of velocity vs [Na] or K1 vs 1/[Na] are linear, suggesting that glutamic acid and sodium are co‐transported on a one‐to‐one basis. t, the sodium concentration giving half maximal velocity of uptake, was found to vary from about 57 mm to 48 mm at glutamic acid concentrations of 1.0–10.0 ± 10−6m. A model of a mechanism by which sodium and glutamate could be co‐transported is presented; the model is in very good agreement with the experimental data.

Uptake of [NMe3H]‐choline by synaptosomes from the central nervous system of Locusta migratoria

“…The role of sodium in choline high-affinity uptake was investigated by replacing Na+ with other monovalent cations. The one-half maximal uptake rate achieved using sodium concentrations between 40 and 6 0 d , was quite similar to values reported by Haga and Noda (1973) for choline accumulation, by Wheeler (1976) for glutamate uptake, and by Martin and Smith (1972) for GABA transport of rat synaptosomes. The observed sodium effect is consistent with 116 BREER the concept that choline uptake is partially driven by the sodium electrochemical gradient (Kuhar and Murrin, 1978;Vaca and Pilar, 1979).…”

The complete rate equation, including the explicit dependence on Na+ ions, for the influx of α-aminoisobutyric acid into mouse brain slices

“…Most studies, where there are sufficient data, indicate that influx is more or less a function of the first power of [Na +] (Eddy, Mulcahy & Thomson, 1967;Inui & Christensen, 1966;Wheeler & Christensen, 1967b;Thomas & Christensen, 1971;Evans, 1973Evans, , 1975Sprott et al, 1975;Wheeler, 1976). Some, like the present one, indicate that it is largely or entirely a function of [Na+] 2 (Vidaver, 1964a;Baker & Potashner, 1971;Peterson & Raghupathy, 1972Wheeler & Hollingsworth, 1978).…”

“…There are four important studies of the Na +-dependent component of L-glutamate influx into nerve preparations. Dependence on the first power of [Na +] was found by Wheeler (1976) for bullfrog (Rana catesbeiana) sciatic nerve, and by Evans for peripheral nerves from the walking legs from crabs (C. maenas) (1973) and for cockroach (P. americana) abdominal nerve cord (1975). Wheeler found that Kt was dependent on [Na +] while I/max was unaffected and furthermore showed that his observations were consistent with the reaction of inactive carrier with Na + to form a 1 : 1 complex which transported glutamate.…”

“…Despite much research with many different preparations including brain slices, spinal cord slices, retina, vertebrate and invertebrate nerve, cultured tissues, cultured cell lines, and synaptosomes and other subcellu~ lar particles, there are only a few detailed studies of the effect of sodium ions on the kinetics of influx of amino acids. Important studies include: uptake of L-glutamate by crab nerve (Baker & Potashner, t971;Evans, 1973); uptake of L-glutamate, L-aspartate and glycine by synaptosomes (Bennett, Logan & Snyder, 1973); uptake of L-glutamate by cockroach nerve cord (Evans, 1975); uptake of GABA I by synaptosomes (Martin, 1973); uptake of L-glutamate by peripheral nerve (Wheeler, 1976); and uptake of Lglutamate by synaptosomes (Wheeler & Hollingsworth, 1978). Of these, only Wheeler (1976), and Wheeler and Hollingsworth (1978) give explicit rate equations with numerical constants for the rate of uptake as a function of both sodium ion concentration and substrate concentration.…”

Cation Dependence of Hypotaurine Uptake in Mouse Brain Slices

“…It is unlikely that sodium ions also enhance the translation rate of either unloaded or hypotaurine-loaded carriers across cell membranes, because the maximal velocities of transport remained about the same. Likewise in synaptosomes and peripheral nerve it was the affinity of the carrier for glutamic acid that was directly affected by sodium rather than the translocation rate of glutamic acid (Bennett et al, 1973;Wheeler, 1976;Wheeler and Hollingsworth, 1978). In contrast, the omission of sodium ions has also been reported to affect the K , more than the V in synaptosornal GABA transport (Martin, 1973).…”