Synaptosomal Ca metabolism studied by electron microprobe analysis

Scanning-transmission electron microscopy coupled with X-ray elemental analysis was used to study air-dried whole mounts of synaptosomes purified from rat caudate. The method of preparation, which was selected to minimize nonphysiological changes in elemental composition of nerve terminals, allowed identification of synaptosomal shape. In addition, cytoplasma and mitochondria could be morphologically distinguished. Elemental X-ray analysis confirmed that the cytoplasm was relatively enriched in Na and Cl, whereas mitochondria were enriched in Ca and P, contained in noncrystalline electron-dense accumulations. Synaptosomes and isolated mitochondria were exposed in vitro to treatments which affect Ca uptake and retention. Changes in the (integrated) intensity of the X-ray spectra for Ca were detected consistent with the predicted effects of these treatments on Ca binding, which was also studied with ⁴⁵Ca as a tracer.