Electron microscopy of the stria vascularis and its response to etacrynic acid. A study using electron-dense tracers and extracellular surface markers.

Lanthanum nitrate (La3+), ruthenium red (RR) and tannic acid (TA) have been used to examine the cell coat and permeability pathways in thin sections of the stria vascularis of normal and etacrynic-acid (EA)-treated guinea pigs. The tight junctions around the stria, at both endolymphatic and spiral ligament sides, excluded tracers even when EA-associated oedema was well advanced. La3+ was also unable to enter oedematous stria from the capillaries. A dense fibrillar coat was revealed on the endolymphatic marginal cell surface. This coat was disorganised during EA intoxication. Both RR and TA crossed the apical membrane and produced enhanced contrast in some, but not all, marginal cells in EA-treated animals. The results suggest that EA may affect the structure of the apical membrane of the marginal cells and that there is heterogeneity amongst the marginal cell population. These possibilities are discussed.