17-BETA-ESTRADIOL IN-VITRO AFFECTS NA-DEPENDENT AND DEPOLARIZATION-INDUCED CA2-BRAIN SYNAPTOSOMES( TRANSPORT IN RAT)

Effects of 17 beta-estradiol (E(2)) in vitro on Na-dependent Ca2+ effl ux from, and depolarization-induced Ca2+ uptake into, the nerve cell w ere studied with the use of synaptosomes isolated from the brain stem, mesencephalic reticular formation (MRF), caudate nucleus and the hipp ocampus of long-term ovariectomized adult female rats. It was found th at E(2) (1) at a concentration of 10 nM or lower, stimulates Na-depend ent Ca2+ efflux in the caudate nucleus and hippocampus, and does not a ffect 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 inv estigated; and (3) produces a biphasic effect on the depolarization-in duced 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 tha t E(2), acting at extranuclear sites, modulates synaptic transmission via alterations of Ca2+ transport mechanisms in nerve endings.