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

Effects of 17beta-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.