The mitochondria play a major role in the regulation of oxidative phosphorylation within the cell. Despite the fact that the enterocytes receive the majority of absorbed phosphate and their high metabolic turnover rate, the role of the intestinal mitochondria in phosphate transport system during maturation is not known. Therefore, the current studies were designed to characterize phosphate transport by jejunal mitochondria of rats during maturation (suckling, weanling, and adolescent rats). The functional integrity of the intestinal mitochondria of suckling and adolescent rats was determined by oxygen consumption studies demonstrating respiratory control ratios of more than 3 when succinate was used as a test substrate. Phosphate uptake was significantly stimulated by the presence of 3 mM ATP at all age groups studied. Maximal phosphate uptake in the presence of 3 mM ATP and 2 mM succinate was 16.5 ± 1.0, 20.5 ± 1 and 28.7 ± 0.4 nmol/mg protein (mean ± SE) in suckling, weanling, and adolescent rats respectively. ATP-dependent phosphate uptake was inhibited by 80% with 100 nM p-MB. Kinetic parameters for ATP stimulated phosphate uptake at 10 s revealed a Km of 4 ± 0.9, 2.8 ± 0.4, and 0.9 ± 0.1 mM and Vmax of 5 ± 0.7, 9.5 ± 1, and 11 ± 0.7 nmol/mg protein per 10 s in suckling, weanling, and adolescent rats, respectively. Phosphate uptake was also stimulated by an inwardly directed pH gradient (pH out < pH inside) compared to no pH gradient condition suggesting the presence of PO4 −/0H− exchange. The kinetic of the PO4 −/0H− exchange showed a Km of 1.9 ± 0.4 and 2.2 ± 1 mM and a Vmax of 1.3 ± 0.4 and 4.4 ±1.5 nmol/mg protein/10 s for suckling and adolescent rats, respectively. Vitamin D deficiency decreased markedly the Vmax and Km of ATP-dependent phosphate uptake in adolescent rats to 1.6 ± 0.2 nmol/mg protein/10 s and 0.2 ± 0.1 mM, respectively. l,25-(OH)2 vitamin D3 administration, 8 h before death increased the Vmax to 3.06 ± 0.8 (p < 0.01) without a significant change in the Km. These results indicate that phosphate uptake into the mitochondria occurs by a ATP-dependent and PO4 −/0H− exchange mechanisms. The ATP-dependent mechanism is regulated by l,25-(OH)2 vitamin D3.
ASJC Scopus subject areas
- Pediatrics, Perinatology, and Child Health