DISTRIBUTION OF MEMBRANE-BOUND GUANYLYL CYCLASES IN HUMAN INTESTINE

The quantification and distinction of human intestine were considered by an enzymatic approach, which comprised . the signal transduction fr om receptor binding to cGMP formation, and, in addition, by showing th e expression of an intracellular portion of these transmembrane protei ns. Basal guanylyl cyclase (GC) activities were 50 to 80 pmol cGMP for mation/min/mg protein and were stimulated up to twofold by heat stable enterotoxin, but were not significantly influenced by atrial natriure tic factor. Enzymatic analysis of colonoscopic specimens pointed to th e prevalence of guanylyl cyclase C in the terminal ileum and in the la rge bowel including colon ascendens, colon descendens, sigmoid, and re ctum. The availability of sequence information on human guanylyl cycla ses permitted the development of a polymerase chain reaction approach for distinguishing the expression of GC-A and GC-C in human tissue sam ples. The expression levels of particulate guanylyl cyclases found by polymerase chain reaction in surgical biopsy specimens confirmed the e nzymatic data, in that substantial expression of GC-C was found not on ly in the small intestine but also in the large bowel. According to th e restriction mapping of amplificates, GC-c prevailed over GC-A throug hout the human intestine, particularly in the mucosal layers.