Triamcinolone acetonide induces transient changes in accumulation and fluxes of calcium in cultured bone cells

The effects of triamcinolone acetonide on the pattern of ⁴⁵calcium efflux were investigated in cultured bone cells. Efflux was measured after equilibrating the cells with ⁴⁵calcium for 24 hours and a short (3 hours) or a long (24 hours) preincubation with the hormone. The results were analyzed by fitting them to a model of three exponential terms, using a computer program based on the non-linear least square method. As reported previously the results indicated the presence of three exchangeable calcium pools which differ in their rates of calcium exchange. A short preincubation with the hormone (3 hours) caused the following changes: (1) A marked increase in the amount of exchangeable calcium in the “slow turnover” calcium pool (S₃) which is probably in the mitochondria. (2) A lesser but significant increase in the amount of calcium in the “fast turnover” calcium pool (S₂) which is probably the calcium in the cytosol. (3) An increase in the rates of calcium exchange between S₂ and the medium (?₂₀) and between S₃ and S₂ (?₃₂). All these changes were transient. After 24 hours of preincubation with triamcinolone acetonide the amounts of calcium in S₂ and S₃ decreased below the control levels and the fluxes were not significantly different from those of the controls.