A B S T R A C T 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 of 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 ['P]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.
We present the 8th case so far published of generalized giant axonal neuropathy. Many features of the neurological picture of this 8 year 8 month old boy were suggestive of progressive bulbar paralysis of childhood. Muscle and sural nerve biopsies disclosed typical nodular axonal swellings measuring between 10--29 nm. Ultrastructure of the inflated portions of the axon consisted almost exclusively of 10 nm filaments. Normally appearing constituents were found in the non-dilated portions of the axons with this particularity that glycogen and mitochondria were aggregated. Previous clinical and pathological evidence indicates that this rare disorder not only affects the peripheral nerves but also the whole CNS. Our case differs from the others reported in literature by its rapidly deteriorating course and by the prominent involvement of some brain-stem motor functions; we offer the theory that a link might be implicated between this entity and Fazio-Londe disease.
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