Ion dependent efflux from neuronal and glial cell cultures

A spontaneous efflux of choline originating from the cytoplasmic free choline compartment and, partly, from metabolized form was measured from neurons and glial cells in culture. The efflux was stimulated by an excess of K⁺ and by the absence of Ca²⁺ ions from the incubation medium in both types of culture. The two effects did not appear to be synergistic.

The stimulation produced by an excess of K⁺ (100 mM) was blocked in neurons by 0.5 μM BaCl₂ and in glia cells by 0.1 μM BaCl₂ (in the presence of 30 mM K⁺). The stimulation produced by the absence of Ca²⁺ instead was not blocked by Ba²⁺ ions in either of the two types of culture. The results suggest that the stimulation induced by K⁺ (high concentration and long time of incubation) might be of biochemical rather than physiological nature and that choline may be driven out of the cells in correlation with the K⁺ gradient. The greater sensitivity of glial cells to K⁺ ions may also suggest a supportive role of these cells with respect to neurons, as they seem capable of furnishing choline for neuronal needs during depolarization.