ULTRASTRUCTURAL, HISTOCHEMICAL AND ELECTROPHYSIOLOGICAL STUDY OF CALFGALLBLADDER EPITHELIUM

Calf (Bos taurus) gallbladder, contrary to that of most mammalian, doe s not concentrate bile. It is to be ascertained whether this phenomeno n is the result of a lack of fluid absorption or a balance between the latter and fluid secretion. To this end we began a characterization o f bovine gallbladder epithelium by means of electron microscopy, immun ocytochemistry, enzymatic activity and electrophysiological measuremen ts. We also partially characterized bile content. The ultrastructural examination showed that surface epithelial cells have the general stru cture that is observed in absorptive epithelia. Mucous secretory activ ity is also evident. Moreover, two distinct types of secreting cells l ine the glands in the lamina propria and contribute to the production of an abundant secretion. The cell surface shows a marked reactivity w ith the anti-alkaline phosphatase serum. Most of the activity of alkal ine phosphatase and L-gamma-glutamyltransferase is found at the apical side of the epithelium. Electrophysiological parameters indicate that this is a low resistance epithelium. Therefore, coexistence of featur es typical of absorptive epithelia and the inability of concentrating bile suggest that, in this organ, fluid absorption and secretion are b oth present.