THE USE OF THE PHOSPHOTUNGSTIC ACID (PTA) AS A STAIN FOR THE PLASMA MEMBRANE

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Abstract
Many investigations on the structure of cell membranes have been carried out on OsO4 or KMnO4 fixed material; however, these procedures fail to demonstrate any basic difference between the various membranes forming the outer coat of the cytoplasm, the endoplasmic reticulum, the nuclear envelope, and the mitochondria. Thus, Robertson (1959) introduced the concept of the unit membrane, 75 Å thick; however, Finean (1961) found that in some specialized cell surfaces the unit membrane is thicker (100–120 Å).The bleaching procedure with strong oxidants solubilizes and removes from the sections the lower osmium oxides (Merriam, 1958) and makes it possible to evaluate a specific stainability, which otherwise would be masked by the overall staining.Marinozzi and Gautier (1961) introduced the use of phosphotungstic acid (PTA) after the bleaching procedure, and noted that the plasma membrane and some pinocytotic vesicles could be preferentially stained. More recently Latta (1962) obtained similar results, staining with PTA sections of tissues embedded in Epon.The present paper deals with the properties and the nature of the PTA staining.

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