Functional specialization of the epithelium in the mesonephric tubules.

An electron microscopy study was aimed to correlate structural differentiation of the epithelium in mesonephric proximal tubules (PT) with the expression of membrane activities of alkaline phosphatase (AP) and 5'-nucleotidase (AMP). Tissue samples of mesonephros were taken from 5 to 16 days old chick embryos. Both enzymes were detected with cerium technique, Mayahara modification of lead capture method was used also for localization of AP. Control incubation was performed with levamisole. The formation of absorptive apparatus was characterized by the differentiation of PT epithelium. Activities of AP and AMP appeared to increase rapidly with the differentiation of epithelium. Reaction products of AP and AMP were detected on brush border as well as on membranes of tubular invaginations, transport tubules and endocytotic vacuoles. The basolateral cell surfaces of epithelium were projected in short interdigitating microvilli and the expression of AP and AMP activities on their membranes suggested the transport role of this structural specialization.