The role of calcium in the regulation of [ 3H]hemicholinium-3 binding sites in rat brain

Abstract

The role of calcium in the regulation of sodium-dependent high-affinity uptake of choline was assessed in vitro in slices of the rat brain, by measuring the specific binding of [ 3H]hemicholinium-3 ([ 3H]HCh-3) and the uptake of [ 3H]choline. Depolarization with potassium of slices of hippocampus, cortex, or striatum significantly increased the specific binding of [ 3H]HCh-3 when compared to control slices. However, the observed potentiation of specific binding of [ 3H]HCh-3 was markedly inhibited by the removal of calcium from the incubation medium in cortex or hippocampus, but not in slices of striatum. Alterations in the uptake of [ 3H]choline directly paralleled the observed changes in the specific binding of [ 3H]HCh-3 in striatum of the rat and were unaffected by the reduction of calcium in the incubation medium. The inorganic calcium channel antagonists, cadmium and cobalt, but not magnesium, zinc, manganese or lanthanum, significantly inhibited the 40 mM potassium chloride-induced stimulation of the binding of [ 3H]HCh-3 in the striatum. Finally, the calcium ionophore A23187 significantly increased the binding of [ 3H]HCh-3 in slices of striatum, either in the presence or absence of calcium in the bathing medium. This study demonstrates regional differences in the role of extracellular calcium in the regulation of the uptake of choline and suggests the involvement of intracellular release of calcium in the in vitro regulation of the sodium-dependent high-affinity uptake of choline in the striatum