Stimulation of Ca2+/Mg2+-ATPase activity in adult rat cerebrocortical synaptosomes by 3-5-3′-L-triiodothyronine

Stimulation of the calcium-stimulated and magnesium-dependent adenosine triphosphatase (Ca2+/Mg2+-ATPase) activity by 3-5-3'-L-triiodothyronine (T-3) in synaptosomes prepared from adult rat cerebral cortex was demonstrated both in vitro and in vivo. T-3 stimulated the Ca2+/Mg2+-ATPase activity in time dependent and dose dependent manner to depolarization-induced intact synaptosomes suspended in Cd2+-loaded choline-chloride buffer, representing involvement of the recovery phase of the changes in intrasynaptosomal Ca2+ level in this activation. T-3 (100nM) also stimulated the enzyme activity in nondepolarized intact synaptosomes suspended in choline-chloride buffer. T-3 had direct and dose-dependent stimulatory effect on the Ca2+/Mg2+-ATPase activity of the lysed synaptosomal suspension. The effect of T-3 on the lysed synaptosomes was higher than that found on the nondepolarized intact synaptosomes. The condition probably represents the direct and/or indirect interaction of T-3 with the enzyme through plasmamembrane related phenomenon that needs further investigation. After T-3 treatment, a dose-dependent activation of the enzyme was found in vivo. It appears that T-3 plays a role on adult brain neuronal Ca2+-mobilization through stimulation of the Ca2+/Mg2+-ATPase activity in nerve terminals.