Mitochondrial Granules in the Liver of Rats Kept on Stable Strontium Supplementation

Abstract

Extensive literature exists on accumulation of divalent cations by liver mitochondria (1–5). The accumulation of strontium by isolated mitochondria was described first by Mraz (6) and Chappell et al. (1,7) in the early 1960s. Detailed studies on Sr2+ uptake by isolated mitochondria have been reported in 1965 by Carafoli et al. (8–10). These investigations on respiring rat-liver mitochondria have revealed several important features of mitochondrial Sr2+ uptake. The accumulation of Sr2+ appears to be an energy-linked process, similarly to the accumulation of other divalent cations, such as Ca2+ (2,4,11), Mg2+ (3,12), and Mn2+ (1,7). According to Carafoli (8), the process of Sr2+ accumulation by isolated mitochondria can be divided into two distinct phases: (a) an initial, rapid phase, with the accumulation of Sr2+ lasting only few seconds (this phase does not require ATP and Mg2+, but does require respiration in the presence of Pi; when respiration is inhibited, this phase may be supported by addition of ATP); and (b) a second, slow phase, which requires respiration in the presence of ATP, inorganic phosphate, and Mg2+. The maximum accumulation of Sr2+ by isolated rat-liver mitochondria can reach 2.5 μmoles Sr2+/mg mitochondrial protein; Sr/Pi accumulation ratio is 1.2–1.4, which does not correspond exactly to the composition of any known form of strontium phosphate (8).