The seasonal distribution of anionic binding sites in the basement membrane of the kidney glomerulus of the winter flounder Pseudopleuronectes americanus.

The blood of the winter flounder, Pseudopleuronectes americanus, contains small (3000-8000 daltons) anionic peptides (pI less than 5) with antifreeze properties. They are present only in the winter and are retained in the circulatory system even though inulin and polyethylene glycol, of comparable molecular size, are filtered by the glomerular kidney. Electron micrographs of flounder-kidney glomeruli revealed that their structure is similar to that of mammals and that cationized ferritin binds at regular 60 nm intervals in the lamina rara interna of the basement membrane as it does in mammals. The binding of cationized ferritin, in conjunction with the previous observation that cationized antifreeze peptides exhibit a marked increase in renal clearance, suggests that an anionic repulsion barrier within the glomerular basement membrane of the winter flounder is responsible for the conservation of the anionic antifreeze peptide molecules found in their blood during the winter. This barrier also appears to be present in summer specimens of the flounder which lack the antifreeze peptide.