QUINACRINE STAINING OF MARGINAL CELLS IN THE STRIA VASCULARIS OF THE GUINEA-PIG COCHLEA - A POSSIBLE SOURCE OF EXTRACELLULAR ATP

There is accumulating evidence for a purinergic humoral system involve d in the control of cochlear function. Evidence of specific P-2 purino ceptors on cochlear tissues implies a role for extracellular adenosine triphosphate (ATP) in the cochlea. To further this hypothesis a study was undertaken to determine if there was any specific source of purin e compounds in cochlear tissues. Cochlear tissues (the sensory epithel ium and lateral wall) from the guinea pig were incubated with the acri dine derivative quinacrine dihydrochloride (5 X 10(-6) M in phosphate- buffered saline for 30 min at room temperature) which fluoresces on bi nding to high concentrations of ATP. Most cochlear tissues showed a di ffuse green fluorescence slightly above the background level. However, a region of the marginal cells of the stria vascularis showed a speci fic punctate fluorescence. Optical sectioning of these cells by confoc al microscopy revealed that the fluorescent structures in these margin al cells was confined to a region up to 10 mu m from their endolymphat ic surface. Similar cells studied by transmission electron microscopy showed membrane-bound vesicles located in the same region of the cell. These data imply that purine compounds are localized in discrete stru ctures, perhaps vesicles, within the marginal cells which could serve as a source of extracellular ATP in the cochlea.