Effect of depolarizing agents on choline acetyltransferase and acetylcholinesterase activities in primary cell cultures of spinal cord

In cultured neurons dissociated from the spinal cord of fetal mouse, high concentrations of KCl (47 mM) increased choline acetyltransferase (CAT) activity up to 5.5-fold but suppressed acetylcholinesterase (AChE) activity to less than half the level of control cells. Veratridine (3 microM) also increased CAT activity 1.6-fold and suppressed AChE activity to the same level as that induced by high KCl. The increase of CAT activity by the depolarizing agents was blocked by Ca2+ antagonists (verapamil and high Mg2+) and in a low Ca2+ medium, whereas the suppression of AChE activity by high KCl was restored by the same procedures. The synthesis of radiolabeled acetylcholine from [14C]choline was also enhanced 4-fold by incubating cells in high KCl medium. Although the uptake of L-[3H]leucine and [14C]choline into the cells was slightly enhanced by high KCl medium, neither the total amount of protein nor the incorporation of L-[3H]leucine into protein was increased by high KCl medium. These observations indicate that depolarization increased CAT activity in a specific manner, that the activities of CAT and AChE changed inversely under several conditions, and that the effect of depolarization presumably was mediated by the entry of Ca2+ into neuronal cells. The findings raise the possibility that trans-synaptic input could play a crucial role in the development of the activity of cholinergic neurons in spinal cord.