Estradiol in vitro modulates Na+-dependent Ca2+ uptake by synaptic plasma membrane vesicles of rat brain regions

Membrane vesicles loaded with [Na+], prepared from synaptosomal plasma membranes (SPM) of whole brains (WB), hippocampi (Hip) and caudate nuclei (NC) of female rats, were used to study Na+ -dependent Ca2+ transport across SPM vesicles under the influence of 17beta-estradiol (E2) in vitro. In concentrations near to physiologic, E2 significantly increased 45Ca2+ uptake by SPM vesicles from all the brain tissues investigated. The maximum increase was observed for WB (21%) and Hip (33%) at 10(-9) mol/l, and for NC (31%) at 5 x 10(-9) mol/l of E2. These results (a) confirm our earlier finding that E2 in vitro modulates Na+-dependent Ca2+ transport across synaptosomal membrane in rat brain regions, and (b) suggest Na+/Ca2+ exchange as principal mechanism of the E2-stimulated Na-dependent Ca2+ uptake by membrane vesicles. The involvement of any ATPases as possible mediators is discussed.