Control of Cation Transport in Cultured Glial Cells by External Ca++: a Possible Signal in Glial-Neuronal Interaction

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Abstract
In cultured glial cells from chick embryonic brain, both influx and efflux of 42K+ and 22Na+ are dependent on the external Ca2+ concentration ([Ca2+]0) between 2-0.1 mM although intracellular concentrations of K+ ([K+]i) and Na+ [Na+]i) do not change. Only a reduction of [Ca2+]0 < 0.1 mM results in both a decrease of [K+]i and an increase of [Na+]i. Ouabain significantly decreases the [Ca2+])0 sensitivity of uphill cation movements (K+ influx and Na+ efflux), while the [Ca2+]0 sensitivity of downhill cation movements (K+ efflux and Na+ influx) is almost not affected by the presence of ouabain. Additionally, a decrease in [Ca2+]0 triggers an increase in intracellular concentration of cAMP. Changes of [Ca2+]0, which takes place in vivo in the microenvironment of the glia after neuronal firing, represent a signal in the glial-neuronal interaction controlling cation transport and that this control is achieved by cooperation between the cAMP-generating and the cation transport system.