Effect of chronic vitamin D deficiency on chick heart mitochondrial oxidative phosphorylation

Chicks were raised for 3 to 4 weeks either on a normal (vitamin D supplemented) or a rachitogenic diet. The Ca 2+ content of the serum, heart tissue and heart mitochondria was significantly decreased in chicks raised on a rachitogenic diet. In mitochondria isolated from calcium deficient hearts, the rate of ADP induced state 3 respiration and 2,4-DNP uncoupled respiration were significantly decreased. Furthermore, the ATP content of heart tissue was significantly decreased in calcium deficient hearts. These data suggest that an overall deficiency in energy production via oxidative phosphorylation exists in chronic calcium deficiency secondary to vitamin D deficiency. When vitamin D deficient chicks were orally dosed with vitamin D 3, serum calcium level and state 3 respiration rate returned to normal indicating that the above changes are reversible. Although previous studies have indicated that excess Ca 2+ has deleterious effects on mitochondria, the results of the present study suggest that optimal mitochondrial function is dependent upon vitamin D dependent phenomena, including maintenance of calcium concentration within a relatively narrow range.