Involvement of phospholipase A2 in the regulation of [3H]hemicholinium-3 binding.
We have examined the effects of exogenous phospholipase A2 (PLA2) on the sodium-dependent high-affinity choline uptake mechanism as assessed by the specific binding of [3H]hemicholinium-3 ([3H]HCh-3). Incubation of striatal synaptic membranes with bee venom PLA2 resulted in a concentration-dependent increase in the specific binding of [3H]HCh-3. The effect of PLA2 on [3H]HCh-3 binding was inhibited by quinacrine, a PLA2 inhibitor, and by removal of calcium. Scatchard analysis revealed that the observed changes in binding reflected a 2-fold increase in both the capacity and affinity of [3H]HCh-3 for its binding site. Choline and N-butylcholine inhibited the specific binding of [3H]HCh-3 in both control and PLA2-treated membranes with similar potency. When a low concentration of PLA2 was incubated with the striatal synaptosomes, a small but significant increase in high-affinity [3H]choline uptake was observed. However, higher concentrations of PLA2, which further increased the specific binding of [3H]HCh-3, caused a reduction of [3H]choline uptake, apparently due to disruption of synaptosomal integrity by PLA2. Finally, potassium depolarization- and PLA2-induced increases in specific [3H]HCh-3 binding were not additive. These results suggest a possible role for endogenous PLA2 in the calcium-dependent regulation of sodium-dependent high-affinity choline uptake.
Yamada
K
K
Department of Psychiatry, Johns Hopkins University, School of Medicine, Baltimore, MD 21205.
Saltarelli
M D
MD
Coyle
J T
JT
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002794:Choline / Q000378:metabolism / Q000493:pharmacokinetics; D003342:Corpus Striatum / Q000166:cytology / Q000378:metabolism; D006426:Hemicholinium 3 / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D010740:Phospholipases / Q000378:metabolism*; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D011796:Quinacrine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism; D013570:Synaptic Membranes / Q000378:metabolism
D006426:Hemicholinium 3; D012964:Sodium; D010740:Phospholipases; D010741:Phospholipases A; D054467:Phospholipases A2; D011796:Quinacrine; D002794:Choline; D002118:Calcium