An evaluation of normal strial capillary transport using the electron-opaque tracers ferritin and iron dextran

Enzymatic tracer techniques to study normal and pathologic strial capillary transport pose various problems. The use of electron opaque tracers can circumvent many of these problems. Iron dextran (mol. diam 20--70 A) and ferritin (mol. diam 110 A) were injected intravenously and the mice sacrificed at intervals of 1/2, 1, 2, 5, and 24 h. The iron dextran results were unusual in that from 1/2 to 5 h after administration the tracer was present within the cytoplasmic matrix of endothelia, but by 24 h it had been cleared out. No transendothelial exchange was noted. The ferritin results were in conflict and previous results using horse-radish peroxidase. Transport of ferritin was minimal regardless of time sacrificed. No more than a few molecules were scattered about the capillary basal limina. Those molecules transported across capillaries were apparently delivered by means of the micropinocytotic system. The results suggest a blood-strial barrier similar to the blood-thymic and blood-myenteric barriers. Experimental as well as control animals exhibited strial light cells which contained ferritin-like particles within their cytoplasmic matrices. These light cells are probably reticuloendothelial type cells. Ferritin may be useful to gauge strial capillary transport alterations associated with auditory pathologies.