Ultrastructural, histochemical and electrophysiological study of calf gallbladder epithelium

Calf (Bos taurus) gallbladder, contrary to that of most mammalian, does not concentrate bile. It is to be ascertained whether this phenomenon 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 of bovine gallbladder epithelium by means of electron microscopy, immunocytochemistry, enzymatic activity and electrophysiological measurements. We also partially characterized bile content. The ultrastructural examination showed that surface epithelial cells have the general structure that is observed in absorptive epithelia. Mucous secretory activity is also evident. Moreover, two distinct types of secreting cells line the glands in the lamina propria and contribute to the production of an abundant secretion. The cell surface shows a marked reactivity with the anti-alkaline phosphatase serum. Most of the activity of alkaline 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 features typical of absorptive epithelia and the inability of concentrating bile suggest that, in this organ, fluid absorption and secretion are both present.