Properties of a Ca2+ and Mg2+ stimulated ATPase in the rat caudate nucleus

Adenosine triphosphatase (ATPase) activity which could be stimulated maximally by either Ca2+ or Mg2+ was identified in a synaptosomal fraction from rat brain caudate nucleus. The thermodynamic properties of the Ca2+ and Mg2+ stimulated enzymes were similar to each other. Oligomycin, sodium azide and dinitrophenol had no significant inhibitory effects on stimulation by either cation. In vitro incubation of the ATPase with cis- or trans-flupenthixol, chlorpromazine or trifluoperazine, but not with haloperidol, significantly inhibited stimulation by either cation. The DA receptor agonist 2-amino-6,7-dihydroxy-1,2,3,4-tetrahydronaphthalene (ADTN) inhibited stimulation of the enzyme by either cation, while d-amphetamine, SKF 38393, pergolide and LY-171555 had no significant effects. Nomifensine at 10(-3) M inhibited the cation stimulation by about 33%. In vivo administration of dopamine (DA) receptor antagonists (haloperidol, cis- and trans-flupenthixol, spiperone, chlorpromazine and trifluoperazine) and the agonist apomorphine neither inhibited nor stimulated ATPase activity. It appears from these data that the ATPase activity is not under DA receptor modulation. In addition, our tentative conclusion is that one enzyme is involved, because both Ca2+ and Mg2+ produced similar maximal stimulations, the activities as a function of temperature were similar, the enzyme could not be further stimulated with Ca2+ after maximal stimulation by Mg2+ (and vice versa), and the behaviour of the ATPase activity to all drugs tested was similar.