Biomedical subjects
Publications and source records attributed to L Hertz.
A specific binding of serotonin (at least 50 fmol/mg protein) was demonstrated in mouse astrocytes in primary cultures. This binding was inhibited by methysergide and by fluoxetine.
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Kinetics for uptake and release of glutamate were measured in normal, i.e., nontransformed, astrocytes in cultures obtained from the dissociated, cortex-enriched superficial parts of the brain hemispheres of newborn DBA mice. The uptake kinetics indicated a minor, unsaturable component together with an intense uptake following Michaelis-Menten kinetics. The Km (50 micrometer) was reasonably comparable to the corresponding values in brain slices and in other glial preparations. The Vmax (58.8 nmol min-1 mg-1 protein) was, however, much higher than that observed in glial cell lines or peripheral satellite cells, and also considerably higher than that generally reported for brain slices. The release of glutamate was much smaller than the uptake, and only little affected by an increase of the external glutamate concentration, suggesting a net accumulation of glutamate rather than a homoexchange. Such an intense accumulation of glutamate into normal astrocytes may play a major role in brain metabolism and may help keep the extracellular glutamate concentration below excitatory levels.
Content of GABA was measured in cultured, normal astrocytes [from the brain cortex of newborn mice] together with the effect of nonradioactive GABA on the efflux of labeled GABA from cells previously loaded with (14C)GABA. An increase of external GABA concentration from 0 to 25 micron evoked a rise of the GABA content in the cells to a level which was approximately 50 times that of the incubation medium. Neither 200 nor 2000 micron nonradioactive GABA had any effect on the rate of release of radioactivity from cells loaded with (14C)GABA. Both the high tissue/medium ratio and the lack of a GABA-induced enhancement of the release of radioactivity indicate that the previously observed high-affinity uptake of GABA in cultured astrocytes represents a net uptake and not a homoexchange with endogenous GABA. This uptake is sodium dependent but was found to be unaffected in potassium-free media; the quantitative correlation between GABA transport and sodium transport differed from that reported for synaptosomes.
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Pentobarbital (0.5-2mM), but not phenobarbital, was found to inhibit the uptake of gamma-aminobutyric acid into mouse astrocytes in primary cultures up to 45%. This inhibition was additive to a reduction in uptake rate caused by excess potassium. Its possible role in the pharmacological action of pentobarbital is discussed.
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Neuroepithelial cells of the presumptive spinal cord (stage 11) consume oxygen, albeit at a low rate. As neurons differentiate in the presumptive motor horns the rate of oxygen consumption increases to approximately 70 mumoles/g wet wt/hr by stage 26. It is suggested that the rate of oxygen consumption per unit volume of neuron then remains constant as subsequent development ensues but since the neurons become more widely spaced the oxygen consumption per unit volume of anterior horn tissue decreases.