Similarity in Uptake and Retention of Trace Amounts of 31 Silicon and 68 Germanium in Rat Tissues and Cell Organelles

Uptake of Si and Ge (chemical analogue of Si) in rat tissues was compared to establish their subcellular localization and determine if Ge could be used to trace Si in situ. 31Si and 68Ge were found in tissues and in cell organelles after injection of 31Si (OH) 4 or 68Ge (OH) 4. Accumulation of 31Si and 68Ge in the tissues increased for 30 minutes, declined rapidly about 30 minutes and then was gradually but steadily depleted. Simultaneous double labelling with 31Si and 68Ge produced concomitant accumulation and release of both isotopes. After a single IP injection, some 68Ge remained in the spleen and kidney for up to 20 days. The 31Si and 68Ge concentration in the tissues and cell organelles increased linearly with the amount administered (31Si, 10-4 to 10-2 g/kg body wt and 68Ge, 10-9 to 10-3 g/kg body wt). Thus, substitution of 68Ge for 31Si can extend the limit of detection of Si by at least 5 orders of magnitude. Both 31Si and 68Ge were water extractable (47%-74% and 38%-89%, respectively) from liver cell organelles; 45%-81% 31Si and 66%-90% 68Ge were extractable in 10% TCA, while only 10%-59% of either isotope were extractable in organic solvents (acetone, chloroform, ethanol). A small percentage of Si may be bound or polymerized.