17β-estradiol in vitro affects Na-dependent and depolarization-induced Ca²⁺ transport in rat brain synaptosomes

Abstract

Effects of 17β-estradiol (E₂) in vitro on Na-dependent Ca²⁺ efflux from, and depolarization-induced Ca²⁺ uptake into, the nerve cell were studied with the use of synaptosomes isolated from the brain stem, mesencephalic reticular formation (MRF), caudate nucleus and the hippocampus of long-term ovariectomized adult female rats. It was found that E₂ (1) at a concentration of 10 nM or lower, stimulates Na-dependent Ca²⁺ efflux in the caudate nucleus and hippocampus, and does not affect the efflux in MRF and brain stem; (2) at concentrations above 10 nM has no effect on the Ca²⁺ efflux in any of the four structures investigated; and (3) produces a biphasic effect on the depolarization-induced Ca²⁺ uptake, increasing it in all structures except MRF at 10 nM concentration, and decreasing it at concentrations higher than 10 nM, irrespective of the structure investigated. These results suggest that E₂, acting at extranuclear sites, modulates synaptic transmission via alterations of Ca²⁺ transport mechanisms in nerve endings.