Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

No presente trabalho, nós desenvolvemos um modelo de mecânica estatística para a dinâmica do cotransporte. Em particular, foram analisados o simporte de lactose e H+ catalisado pela LacY, e o antiporte de triose-P e Pi catalisado pelo TPT. Em ambos os casos, nosso ponto de partida foi determinar a curva de energia livre do ciclo de transporte com base na estrutura bioquímica de cada estado. Então, usando o algoritmo de Metropolis em um modelo do caminho aleatório não-homogêneo, nós determinamos a dinâmica do ciclo expressa na curva de energia livre obtida anteriormente. Tanto no caso da LacY quanto no caso do TPT, a concordância entre as predições do nosso modelo e os dados experimentais sugere que a nossa curva de energia livre é apropriada para descrever os processos de transporte através da membrana plasmática. / In the present work, we developed a statistical mechanical model for the dynamics of cotransport. In particular, the symport of lactose and H+ and the antiport of triose-P and Pi were analyzed. In both cases, our starting point was to determine the free-energy curve of the transport cycle based on the biochemical structure of each state. Then, using the Metropolis algorithm in a nonhomogeneous random walk model, we determined the dynamics of the cycle expressed in the free-energy curve obtained previously. Both in the case of LacY and TPT, the agreement between our model predictions and the experimental data suggests that our free-energy curve is appropriate for describing the transport process across the plasma membrane.

Recognising that NPT2 is the major Na/Pi cotransporter in the kidney, that hereditary hypophosphatemic rickets with hypercalciuria (HHRH) is caused by a renal Pi leak and, that Npt2 knockout mice demonstrate a biochemical phenotype similar to that of patients with HHRH, we sought to determine whether NPT2 was a candidate gene for this disorder. Using single-strand conformation polymorphsim (SSCP) analysis and sequencing in six unrelated pedigrees with the disease, we found no disease-causing mutations. Two polymorphisms were identified in the gene and used as markers to examine segregation of NPT2 with the disease. HHRH did not segregate with the gene markers. In addition, the impact of NPT2 on bone mineral density (BMD) was examined by genotyping a population of 104 individuals for which BMD data was available, and determining whether there was an association between NPT2 genotype and bone density. No significant association was found between NPT2 genotype and BMD.

Mice homozygous for the disrupted renal type 11a sodium/phosphate (Na/Pi) cotransporter gene, Npt2, (Npt2 KO) exhibit renal Pi wasting and hypercalciuria, predisposing factors for renal stone formation. We observed that Npt2 KO mice, but not wild-type littermates form renal stones. The renal stones were evident in newborn, weanling and adult mice and composed of calcium (Ca) and Pi. The presence of renal calcification correlated with the absence of Npt2 gene expression and the presence of genes responsible for the synthesis (1alpha-hydroxylase) and catabolism (24-hydroxylase) of 1,25-dihydroxyvitamin D, whose elevated levels contribute to the hypercalciuria and renal calcification in Npt2 KO mice. The renal calcification was associated with increased osteopontin (OPN) mRNA expression and colocalized with OPN, the latter associates with renal stones in vivo and inhibits Ca mineralization in vitro). These data demonstrate that hyperphosphaturia and hypercalciuria, secondary to Npt2 gene disruption, are sufficient for the development of renal calcification.

The developmental profiles of mRNA and protein expression for ornithine decarboxylase (ODC), the Na$ sp+$-dependent glucose co-transporter (SGLT1), sucrase isomaltase (SI), and the Na$ rm sp+K sp+$ ATPase $ alpha sb1$ and $ beta sb1$ subunit isoforms in the postnatal rat small intestine, as well as the effects of exogenous spermidine on their precocious development, were examined. Postnatal age had a significant effect with all enzymes and the nutrient transporter maturing around weaning. Consecutive exposure to exogenous spermidine during suckling precociously induced ODC mRNA, SI protein, and SGLT1 gene expression in the proximal and distal small intestine. Levels of Na$ rm sp+K sp+$ ATPase $ alpha sb1$ and $ beta sb1$ subunit isoform mRNA were precociously induced in the proximal small intestine only. These findings show that exposure to exogenous spermidine can promote precocious alterations in intestinal enzyme and nutrient transporter expression; however, it appears that spermidine must be continuously supplied for these alterations to persist in suckling rats.

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Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

No description available.