Thyroid status influences calcium ion accumulation and retention by rat liver mitochondria

Ca2+ accumulation and retention by isolated rat liver mitochondria (RLM), measured with a Ca2+ electrode as aCa, are markedly influenced by thyroid status. RLM from propylthiouracil (PTU)-fed rats took up Ca2+ from a suspending medium (SM) until 10.26 +/- 2.51 (SD) x 10(-5) M Ca2+ had been added (n = 5). RLM from PTU rats given T3 (100 micrograms/kg daily x 6) showed uptake only until 2.37 +/- 0.59 x 10(-5) M Ca2+ had been added (n = 6) and RLM from normal rats showed uptake until 3.69 +/- 0.53 x 10(-5) M (n = 9) Ca2+ was reached. RLM from the three animal groups lowered the aCa in the SM from 9.13 +/- 1.69 x 10(-6) to 4.96 +/- 2.08 x 10(-6) M regardless of hormonal status. The time in minutes that the aCa remained below the initial level in the rat groups was PTU 94.8 +/- 26.2, PTU + T3, 11.5 +/- 3.9, and normal 26.7 +/- 3.8. All differences were significant at the 0.001 level (ANOVA). bGH did not affect Ca2+ handling by RLM from PTU rats. Administered T3 increased RLM alpha-glycerophosphate dehydrogenase activity 24-36 hr before normalizing Ca2+ handling. The thyroid hormone-sensitive system described here adjusts the SM Ca2+ concentration to a level far above cytosolic so that its function may be to regulate intramitochondrial [Ca2+]. The level of intramitochondrial Ca2+ may be of importance in the mechanism of action of thyroid hormone.