Distribution of Membrane Bound Guanylyl Cyclases in Human Intestine

Abstract

The quantification and distinction of particulate guanylyl cyclases in the human intestine were considered by an enzymatic approach, which comprised the signal transduction from receptor binding to cGMP formation, and, in addition, by showing the expression of an intracellular portion of these transmembrane proteins. Basal guany- lyl cyclase (GC) activities were 50 to 80 pmol cGMP formation/min/mg protein and were stimulated up to twofold by heat stable enerotoxin, but were not significantly influenced by atrial natriuretic factor. Enzymatic analysis of colonoscopic specimens pointed to the prevalen-ce of guanylyl cyclase C in the terminal ileum and in the large bowelincluding colon ascendens, colon descendens, sigmoid, and rectum. Theavailability of sequence information on human guanylyl cyclases per- mitted the development of a polymerase chain reaction approach for distinguishing the expression of GC-A and GC-C in human tissue samples. The expression levels of particulate guanylyl cyclases found by polymerase chain reaction in surgical biopsy specimens con- firmed the enzymatic data, in that substantial expression of GC-C was found not only in the small intestine but also in the large bowel. According to the restriction mapping of amplificates, GC-C pre- vailed over GC-A throughout the human intestine, particularly in the mucosal layers.