Effect of external high potassium and pH on the uptake of choline in glial and neuronal cells in culture.

The Vmax of the uptake of choline was increased in nerve cell cultures by lowering (from 7.4 to 6.5) or increasing (from 7.4 to 8.1) the pH. In neurons no effect was observed on the value of the Km's of the uptake of either the apparent high or low affinity components. In glial cells only a low affinity component was measured at pH 6.5 and diffusion was observed at pH 8.1. An excess of K+ ions in the incubation medium reproduced the increase in Vmax observed with changes in pH suggesting a possible dependence of the uptake of choline upon the H+ and OH- gradients. Taking into account the characteristics already known of the transport of choline into nerve cells, such a dependence adds new insight in the mechanisms underlying the transport and indicates another possible regulation of choline entry, eventually directed towards the synthesis of acetylcholine.