Effects of amino acids on calcium uptake by glial and neuroblastoma cells

Calcium chelators enhance the efflux of taurine from brain slices

Efflux of exogenous [3H]taurine from superfused slices of cerebral cortex of rat was enhanced by the calcium chelators EDTA and EGTA and by large concentrations of unlabelled taurine and histidine. The enhancement by EDTA and EGTA could be totally blocked by excess calcium, but that by the amino acids only partially. The enhancement of spontaneous taurine release in the absence of calcium complicates the assessment of the calcium dependence of evoked taurine release.

Kainate, N-methylaspartate and other excitatory amino acids increase calcium influx into rat brain cortex cells in vitro

Kainate (0.62-5 mM) was found to increase the initial rate of influx of 45Ca and of 22Na into the non-inulin space of rat thin brain cortex slices incubated in vitro, and to shorten the equilibration time for both these ions. N-methyl-DL-aspartate (50-1000 microM), L-glutamate (0.62-5 mM), DL-homocysteate (0.62-2.5 mM), and ibotenate (6-170 microM) also significantly increased the influx of 45Ca into the non-inulin space of this preparation, while the non-neurotoxic acidic amino acids N-acetyl-L-aspartate, and alpha-methyl-DL-aspartate (both 1.25-5 mM), did not increase such influx. We suggest that enhanced calcium uptake may represent the basis for the neurotoxic effects of these compounds.

Effects of neurotransmitters on calcium efflux from cultured glioma cells

The effects of various neurotransmitters and cyclic nucleotides on 45Ca2+ efflux in cultured human glioma cells were investigated. Glutamate and glycine, but not GABA, stimulated 45Ca2+ release from the cells. Stimulation of beta-adrenergic receptors but not alpha-adrenergic receptors also increased 45Ca2+ efflux. Cholinergic receptor stimulation by carbachol had the same effect. The stimulatory effect of carbachol was abolished in the presence of either atropine or hexamethonium. C-AMP and c-GMP increased the 45Ca2+ efflux, suggesting that these agents are involved in the transmitter-stimulated release of 45Ca2+ from the cell. Kinetic analysis of the efflux revealed four calcium compartments. The carbachol-stimulated efflux represented a net release of calcium and could be ascribed to the slowest compartment. The physiological role of the transmitter-stimulated calcium release is discussed in terms of calcium-regulated stimulus-response coupling in glial-neural interaction during excitation.