Adenylate and guanylate cyclase activities and cellular differentiation in rat small intestine

Adenylate and guanylate cyclase activities were measured in rat small intestinal villus and crypt cells to determine possible correlations with cellular differentiation. Isolated intestinal cells were prepared by a method which effectively separates differentiated villus cells from undifferentiated crypt cells (J Biol Chem 248:2542, 1973). Crypt cells were found to have a significantly lower guanylate cyclase activity than villus cells. Adenylate cyclase activity was higher in crypt cells than villus cells, although the difference was less striking than the reverse gradient observed for guanylate cyclase. There was no gradient of activity for cyclic guanosine 3':5'-monophosphate phosphodiesterase. However, cyclic adenosine 3':5'-monophosphate phosphodiesterase activity was lower in villus cells. No villus to crypt gradient of cyclic adenosine 3':5'-monophosphate concentration was detected in mucosa frozen rapidly in liquid nitrogen. The properties and subcellular localization of the cyclases were also evaluated, and of particular interest was the localization of guanylate cyclase to the microvillus membrane and the confirmation of adenylate cyclase activity in the lateral-basal membrane. The villus to crypt gradient of guanylate cyclase suggests that this enzyme has a specialized role in the differentiated villus cell. The contrasting subcellular localization of the cyclases suggests that the cyclases may be interrelated, possibly reflecting the epithelial cell polarity for absorption and secretion.