Histochemical demonstration of the heterogeneity of the epithelium of proximal tubules in the chick mesonephros

Summary al tubules (PT) in 7–10-day old chick mesonephros were examined histochemically to evaluate their structural and functional properties related to the absorption capacity of the epithelium and its possible alterations leading to cystically dilated tubules (CDT). Alkaline phosphatase activity at the apical cell membrane was demonstrated in varying intensities in large PT. A similar heterogeneity was also detected in the expression of proteoglycans (Lewisx antigen) localized in the apical part of the epithelial cell membrane but not in the basolateral membrane parts (β-catenin, Na+,K+-ATPase). In analogy, the ability to accumulate trypan blue was found in the same cell population. We hypothesize that epithelial cells in proximal tubules of nephrons with a defective apical cell membrane cause reduced fluid absorption and subsequent overfilling and dilation of the tubules.