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

In cultured glial cells from chick embryonic brain, both influx and efflux of 42K+ and 22Na+ are dependent on the external Ca++ concentration ([Ca++]₀) between 2 and 0.1 mM although intracellular concentrations of K+ ([K+]i) and Na+ ([Na+]i) do not change. Only a reduction of [Ca++]₀ below 0.1 mM results in both a decrease of [K+]i and an increase of [Na+]i. Ouabain significantly decreases the [Ca++]₀ sensitivity of uphill cation movements (K+ influx and Na+ efflux), while the [Ca++]₀ sensitivity of downhill cation movements (K+ efflux and Na+ influx) is almost not affected by the presence of ouabain. Additionally, a decrease in [Ca++]₀ triggers an increase in intracellular concentration of adenosine 3'':5''-cyclic monophosphoric acid (cAMP). These findings suggest that changes of [Ca++]₀, which take 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 a co-operation between the cAMP-generating and the cation transport system.