Thyroid Status Influences Calcium Ion Accumulation and Retention by Rat Liver Mitochondria

Abstract

Abstract

Ca²⁺ accumulation and retention by isolated rat liver mitochondria (RLM), measured with a Ca²⁺ electrode as a _Ca, 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) × 10^-5 MCa²⁺ had been added (n = 5). RLM from PTU rats given T ₃ (100 μg/kg daily × 6) showed uptake only until 2.37 ± 0.59 × 10^-5 MCa²⁺ had been added (n = 6) and RLM from normal rats showed uptake until 3.69 ± 0.53 × 10^-5 M(n = 9) Ca²⁺ was reached. RLM from the three animal groups lowered the a _Ca in the SM from 9.13 ± 1.69 × 10^-6 to 4.96 ± 2.08 × 10^-6 M regardless of hormonal status. The time in minutes that the a _Ca remained below the initial level in the rat groups was PTU 94.8 ± 26.2, PTU + T ₃, 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 T ₃ increased RLM α-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.