Abstract
Thin slices of guinea pig cerebral cortex incubated for 30-60 min with or without ouabain were analyzed for Na+, K+ and inulin contents. Other brain slices treated in a similar manner were fixed in potassium pyroantimonate-containing buffered glutaraldehyde solution and examined in the electron microscope. Slices incubated in the presence of ouabain contained considerably more Na+ in the non-inulin, presumably intracellular, space. However, precipitates of pyroantimonate which have been accepted by some to indicate the site of Na+ localization were almost entirely restricted to the extracellular space in both the control and experimental slices and appeared to reflect the method of fixation by immersion and not the movement of Na+. It is our conclusion that the lack of correlation between the chemical localization of Na+ and the pyroantimonate technique is due to the limitation of the latter method.