Membrane permeability as a cause of transport defects in experimental Fanconi syndrome. A new hypothesis.
AUTOR(ES)
Bergeron, M
RESUMO
The injection of sodium maleate (200-400 mg/kg) into rats produces aminoaciduria along with glycosuria and phosphaturia, resembling the Fanconi syndrome. This experimental model was studied by means of microinjections into proximal convoluted tubules of the kidney, stop-flow diuresis, and microperfusion of single nephrons. Our results show that, in maleate-treated rats, competition between amino acids or related structures (L-proline, L-OH-proline, and glycine) possesses the same characteristics, and net influx of amino acids appear normal at the proximal nephron. Data obtained by classical stop-flow techniques and single nephron microperfusions also indicate a normal entry of labeled amino acids (L-lysine, glycine, L-valine, L-proline, L-cystine), and 3-0-methyl-D-[3H]glucose and [32P]phosphate from the luminal side of the proximal tubule cell. However, the efflux of molecules from the cell appears enhanced throughout the proximal and distal tubule; molecules that exit at this site are excreted directly into the urine. Our results suggest that the phosphaturia, aminoaciduria, and glycosuria of the experimental Fanconi syndrome can be explained by a modification of the cell membrane permeability (increased efflux) at distal sites of the nephron rather than by a modification of the membrane transport (decreased influx) at the proximal sites, as is currently accepted. Our data also stress the importance of efflux phenomena in membrane transport.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=436771Documentos Relacionados
- The cause of neural tube defects: some experiments and a hypothesis.
- Cellular sodium transport and hypertension: a new hypothesis.
- Dysregulation of strongyloidiasis: a new hypothesis.
- Gravitational field enhances permeability of biological membranes to sucrose: an experimental refutation of sucrose-space hypothesis.
- The aetiology of mirror writing: a new hypothesis.