Which staining method is commonly used to highlight basement membranes in tissue sections?

• A. PAS
• B. Alcian blue pH 2.5
• C. Colloidal iron
• D. Crystal violet

Answer: (A)

Periodic acid–Schiff (PAS) staining highlights basement membranes because they are rich in carbohydrate-containing substances such as glycoproteins and proteoglycans. PAS works by oxidizing sugars with periodic acid to form aldehyde groups, which then react with the Schiff reagent to yield a magenta color. This makes the basement membrane visibly distinct along the periphery of structures like blood vessels and glomeruli. That specificity for carbohydrate-rich basement membranes is why PAS is the standard method for visualizing them in tissue sections. The other stains target different components: Alcian blue at pH 2.5 stains acidic mucopolysaccharides and mucins blue; colloidal iron also highlights acidic polysaccharides but is less specific for basement membranes; crystal violet is a general dye used for nuclei or Gram staining contexts, not for basement membranes.