On the occurence and composition of dense particles in mitochondria in ultrathin frozen dry sections.

Clusters of dense particles were observed irregularly in mitochondrial profiles of shock-frozen brown adipose tissue and liver when cryosectioned at a chamber temperature of -80 degrees C and not if sectioning was performed at -110 degrees C. The particles are rich in Ca and P (Ca/P =0.5); they are therefore not any form of tricalcium orthophosphate (e.g. hydroxyapatite). They apparently form by electrolyte diffusion in the section and therefore cannot be considered as representing the in vivo pool of mitochondrial calcium.