Calcium fluxes in cultured and bulk isolated neuronal and glial cells.

— The influx and efflux of 45Ca has been studied in cultured human glioma and mouse neuroblastoma cells and in isolated fractions enriched in synaptosomes, neuronal and astrocytic perikarya from rabbit brain. The uptake of 45Ca was somewhat more efficient in glioma compared to neuroblastoma cells, whereas there was little difference in the rate of 45Ca uptake by isolated glial cells and neuronal perikarya. Isolated synaptosomes showed the highest rate of 45Ca accumulation. An increase of K concentration to 50 mm in the medium, with a corresponding lowering of Na, stimulated both glioma and glial as well as synaptosomal 45Ca uptake more markedly than the uptake by neuroblastoma cells and neuronal perikarya. Lowering the Na concentration and replacing it by choline had no effect on the cultured cells and astrocytes. Na-free media caused massive stimulation of 45Ca influx in all fractions and cells tested. The efflux of 45Ca was studied after preloading of cells. Three phases could be resolved from the desaturation curves. All cells had nearly similar half-lives for 45Ca efflux under standard conditions. Pulses of media containing 50 mm-K stimulated 45Ca efflux from glioma cells and astrocytes more efficiently than from neuroblastoma cells, neuronal perikarya and synaptosomes. The stimulated release was exclusively seen in Ca-containing media in experiments with the cultured cells and in Ca-free media in experiments with cell perikarya. The effect of transmitter pulses on the release of 45Ca was examined in a limited series. Acetylcholine and isoproterenol were found to stimulate 45Ca release more actively from glia than from neurons.