GABA Efflux Research Articles

The spontaneous and electrically evoked release of [ 3H]-GABA from the isolated hemisected frog spinal cord

A study has been made of the spontaneous and electrically evoked release of [ 3H]GABA from the isolated, hemisected spinal cord of the frog. The spontaneous efflux of radioactive GABA was exponential with time and was significantly increased by ouabain, p-hydroxy-mercuribenzoate, l-2,4-diaminobutyric acid and also by nonradioactive GABA; of the convulsants investigated, only strychnine affected (reduced) release. Electrically evoked release could only be achieved by stimulation of descending spinal tracts; release was calcium-dependent and was a function of the stimulation frequency, duration and applied current employed. The evoked release was inhibited by ouabain, p-hydroxy-mercuribenzoate and picrotoxin, significantly potentiated by bicuculline whereas strychnine was without effect. The actions of these drugs could not be explained on the basis of their effects on the uptake of [ 3H]GABA by spinal cord tissue. The results suggest that GABA may act as a neurotransmitter in the spinal cord. Furthermore, it is concluded that the actions of picrotoxin and bicuculline on [ 3H]GABA release are not solely the result of GABA receptor blockade.

The efflux of 45Ca 2+ and [ 3H]γ-aminobutyric acid from cat cerebral cortex

The efflux of both 45Ca 2+ and [ 3H]GABA from suprasylvian cortex of cat has been studied in vivo. After pre-incubating the cortex with radioactivity for 90 min, superfusion with non-radioactive medium was carried out using 0.8 ml vol. changed at 10 min intervals. Increases in the calcium concentration of the medium resulted in greater efflux of both 45Ca 2+ and [ 3H]GABA, and the effect on [ 3H]GABA efflux was potentiated by AOAA. The effect of a 1mM increment in Ca 2+ concentration was only slightly less than that of a 20mM increment. Adding Mg 2+ to the medium did not produce increases comparable to added Ca 2+, whereas electrical stimulation of the cortex had no effect on the efflux of either 45Ca 2+ or [ 3H]GABA. Thiosemicarbazide, an epileptogenic agent, resulted in a slightly irregular efflux of 45Ca 2+ with peaks visible at times of seizure activity. The efflux of 3H 2O and 14C-(car☐yl)-inulin could not be correlated with any of the above treatments. The efflux of [ 3H]GABA from the cortex is considered to originate from synaptic terminals and that of 45Ca 2+ may be the result of reactions at the membrane triggering the release or turnover of calcium.

The efflux of radioactive GABA from rat retina in vitro

Rat retinae were loaded with radioactive GABA in vitro and the efflux of this compound then studied. The loss of radioactivity occurred in three stages with widely different rate constants. Efflux was considerably reduced when GABA metabolism was inhibited by amino-oxyacetic acid. Significantly more GABA, and less of its metabolites, were released by dark-adapted retinae as compared with those in the light. No modification of the release process was observed, however, during subsequent illumination of these retinae. Raising the K + concentration of the perfusing medium to 60 mM caused a pronounced rise in GABA output lasting 15–20 min. A similar response was evoked by electrical field stimulation of the retinae, and neither process was altered by the omission of Ca 2+ from the incubating medium.

Efflux of amino acid neurotransmitters from rat spinal cord slices. I. Factors influencing the spontaneous efflux of [ 14Cglycine and 3H-GABA

The efflux from nervous tissue of presumptive amino acid transmitters was studied by superfusing rat spinal cord slices preloaded with [ 14Cglycine and 3H-GABA. The rate of efflux of the amino acids was slower than that of urea and was retarded by superfusion at 4°C. Extracellular glycine exchanged with intracellular [ 14Cglycine, but did not affect the rates of efflux of labeled GABA, proline, l-lysine, or cycloleucine. The efflux of [ 14Cglycine was accelerated by extracellular GABA, unaffected by extracellular AIB or proline, and retarded by extracellular l-lysine and l-leucine. Ouabain increased the rate of efflux of [ 14Cglycine and 3H-GABA, but did not affect [ 14Curea efflux. Cyanide stimulated the efflux of [ 14Cglycine but not 3H-GABA. The rates of efflux of both amino acids were increased in Ca-free medium containing EDTA, unchanged in30 m M K medium, and decreased in low Na medium. The results indicate that there are mediated transport systems with considerable specificity which regulate the efflux of glycine and GABA across neural membranes.

Efflux of amino acid neurotransmitters from rat spinal cord slices. II. Factors influencing the electrically induced efflux of [ 14Cglycine and 3H-GABA

Electrical stimulation of rat spinal cord slices superfused in vitro produced a greater than two-fold increase in the rate of efflux of glycine and GABA. No urea was released by electrical stimulation. There was a small increase in the rate of efflux of proline, llysine, and cycloleucine, a somewhat greater increase in the rate of efflux of glutamic acid, but the only other amino acid that compared to glycine and GABA in extent of release was taurine. No regional specificity of electrically induced release was found for glycine or GABA, whereas there was a significantly greater release of glutamic acid from cerebral cortex than from spinal cord or cerebellum. High potassium (30–60 m M) or low sodium (28 m M) in the superfusion medium did not influence the electrically stimulated release of glycine or GABA from spinal cord slices. Incubation of slices in standard medium followed by superfusion with Ca-free medium had no effect on stimulated release of labeled glycine or GABA. However, when the slices were incubated and superfused in Ca-free medium containing 2 m M EDTA there was a marked reduction in electricity stimulated release of glycine and GABA. Superfusion with 1 m M strychnine had no effect. Cyanide reduced the release of glycine but not of GABA. Ouabain in the superfusion medium Completely abolished the release of glycine and GABA with electrical stimulation.

Effects of potassium and glutamate on brain cortex slices: uptake and release of glutamic and other amino acids.

Abstract— Effects of an increased concentration of K+ (55 mm) in the medium on fluxes of glutamate and other amino acids in the presence and absence of 10 mm‐glutamate were studied. The following observations were made:(1) The efflux of glutamate is slightly increased by excess K+. The glutamate efflux is smaller than the potassium fluxes.(2) The K+‐induced increase of glutamate efflux is enhanced under anoxia or in glutamate‐containing media.(3) The influx of glutamate is unaffected or slightly increased by excess K+.(4) The efflux of GABA is increased by excess K+, both in the absence and in the presence of glutamate.(5) Efflux of glutamine, leucine and lysine is increased by excess K+, but only provided that glutamate is also present in the medium.(6) Efflux of glutamate and of GABA is increased by addition of 10 mm‐glutamate.

Effects of imipramine on the na +-dependent exchange and retention of γ-aminobutyric acid by mouse brain subcellular particles

The effects of imipramine were investigated with respect to exchange and net content of γ-aminobutyric acid (GABA) in mouse brain subcellular particles in the presence of Na + at 2°. The effects of chlorpromazine and orphenadrine on the system were also investigated. Evidence is presented indicating an inhibition by these three drugs of the Na + -dependent binding of GABA to sites on the membrane which mediate a transmembrane flux of GABA. In the presence of greater concentrations of these drugs a pronounced increase in a nonmediated efflux of endogenous GABA from particles was detected. Studies of the binding of tritiated imipramine demonstrated a complex relationship to drug concentration, indicative of two distinct uptake processes. This paper discusses the possible correlation between the two components of the imipramine binding and the effects of the drug on the exchange and net release of GABA by the particles.