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

Abstract

Stimulation of the calcium-stimulated and magnesium-dependent adenosine triphosphatase (Ca2+/Mg2+-ATPase) activity by 3-5-3′-L-triiodothyronine (T3) in synaptosomes prepared from adult rat cerebral cortex was demonstrated both in vitro and in vivo. T3 stimulated the Ca2+/Mg2+-ATPase activity in time dependent and dose dependent manner to depolarization-induced synaptosomes suspended in Ca2+-loaded choline-chloride buffer, represented involvement of the recovery phase of the changes in intrasynaptosomal Ca2+ level in this activation. T3 (100nM) also stimulated the enzyme activity in nondepolarized intact synaptosomes suspended in choline-chloride buffer. T3 had direct and dose-dependent stimulatory effect on the Ca2+/Mg2+-ATPase activity of the lysed synaptosomal suspension. The effect of T3 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 T3 with the enzyme through plasmamembrane related phenomenon that needs further investigation. After T3 treatment, a dose-dependent activation of the enzyme was found in vivo. It appears that T3 plays a role on adult brain neuronal Ca2+-mobilization through stimulation of the Ca2+/Mg2+-ATPase activity in nerve terminals.