DIAZEPAM ENHANCES INTRASYNAPTOSOMAL FREE CALCIUM CONCENTRATIONS

Synaptosomes prepared from brains of rats were incubated in different concentrations of diazepam under conditions designed to reduce the action of a reversed Na+/Ca2+ exchanger. In synaptosomes depolarized in the presence of added Ca2+, doses of diazepam ranging from 0.1 to 100-mu-M were found to significantly enhance Ca2+ levels measured with the fluorescent dye fura-2, compared to control incubations without drug. Furthermore, doses of diazepam as low as 1-mu-M significantly increased the concentration of Ca2+ in non-depolarized synaptosomes without added Ca2+ in the medium. The effects of depolarization and diazepam treatment were synergistic increasing the levels of intrasynaptosomal Ca2+.