Specificity of the activation of [3H]hemicholinium-3 binding by phospholipase A2

K Yamada, MD Saltarelli and JT Coyle

Department of Psychiatry, Johns Hopkins University School of Medicine, Baltimore, Maryland.

Phospholipase A2 (PLA2) treatment has been shown previously to stimulate the sodium-dependent high-affinity choline uptake system as assessed by both the specific binding of [3H]hemicholinium-3 ([ 3H]HCh- 3) and the uptake of [3H]choline. In the present study, the specificity of PLA2-induced stimulation upon [3H]HCh-3 binding has been examined. PLA2, as well as phospholipase C (PLC), treatment of synaptic membranes produced a dose-dependent increase in the specific binding of [3H]HCh-3 whereas neither phospholipase B nor phospholipase D had any effect. PLC- induced stimulation of [3H]HCh-3 binding resulted from a significant decrease in the Kd without a change in the maximum binding of [3H]HCh-3 binding. PLC treatment of synaptosomes resulted in an inhibition of [3H]choline uptake accompanied by an inhibition of Na+, K+-adenosine triphosphatase activity. In contrast to the increase of [3H]HCh-3 binding, the specific binding of both [3H]desipramine and [3H]mazindol was decreased by PLA2 treatment. After PLA2 treatment, [3H]HCh-3 binding was increased about 2.5-fold over basal levels in different regions of the brain. Electrolytic lesions of the medial septal nucleus and kainic acid-induced lesions of the striatum resulted in a marked reduction of [3H]HCh-3 binding in the hippocampus and the striatum, respectively. Residual [3H]HCh-3 binding in the denervated hippocampus and lesioned striatum was increased by PLA2 treatment but remained lower than that in PLA2-treated controls. Finally, atropine-induced up- regulation of [3H]HCh-3 binding in vivo was not additive with PLA2- induced stimulation. These results support the hypothesis that PLA2 might be involved in the regulation of the sodium-dependent high- affinity choline uptake.

Volume 249, Issue 3, pp. 836-842, 06/01/1989
Copyright © 1989 by American Society for Pharmacology and Experimental Therapeutics

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