A high affinity calcium-stimulated ATPase in synaptic plasma membranes detectable in the presence and absence of exogenous magnesium

Inhibition of mitochondrial Na-dependent Ca2+ efflux from rat brain stem by 17β-estradiol

The role of membrane-bound estradiol in modulation of mitochondrial Ca2+ flux in nerve endings isolated from rat brain stem was examined. Physiological concentrations of 17?-estradiol bind specifically to isolated mitochondria (Bmax 33.8 ? 2.5 fmoles estradiol/mg of protein, Km 0.185 ? 0.006 nmoles/l free estradiol). At concentrations ranging from 1 x 10-10 to 2 x 10-9 moles/l, estradiol significantly (by 23-28%) decreases mitochondrial Na-dependent calcium efflux. Decreased calcium efflux was associated with increased affinity of the Na+/Ca2+ exchanger for Na+ and decreased capacity of the exchanger to extrude Ca2+. Calcium ion efflux modulation and mitochondrial ion retention may be the way that 17?-estradiol exerts its role in nerve cell homeostasis.