Guanylate cyclase C (GC-C) mediates calcium-activated duodenal mucosal bicarbonate secretion

Abstract

Activation of GC-C by heat stable toxin of E. coli (STa) acts via cGMP resulting in duodenal Cl and HCO:; secretion (DMBS). It has been proposed that cGMP regulates increases in [Ca We previously demonstrated in GC-C knockout mice that absence of functional GC-C results in decreased DMBS in vitro in response to STa and PGEz (Gastroenterology 1999;116:A890). The purpose of these studies was to determine whether GC-C (likely cGMP) mediates Ca-induced DMBS. Bicarbonate secretion was quantitated in vitro using a murine knockout model (GC-C gene-ablated; GC-C -1-), and the results contrasted to normal littermates (GC-C +J+). The proximal 8 mm of duodenum was resected and the stripped mucosa mounted in Ussing chambers under short-circuited conditions. The mucosal (HCO:;-free) and serosal (HCO;-containing) sides were bathed in modified Ringer's at 37°C. Basal HCO; secretion and Iso were measured for 20 min and then stimulated with either carbachol (10-4M), the calcium ionophore A23187 (10-5M), or thapsigargin (10AM) to increase [Ca [separate tissues (N = 5), additions to the serosal bath]. Compared to GC-C +1+, carbacholand A23187-stimulated DMBS were markedly (P < 0.01) impaired in GC-C -1tissues (Table, *=P <0.01 vs GC-C+I+). In contrast, thapsigargin-induced increases in DMBS were similar in GC-C -1and GC-C +1+ (Table). The I, responses corresponded with DMBS. While release of intracellular Ca'2+ stores by thapsigargin increased DMBS in GC-C -1similar to GC-C +1+ tissues, DMBS remained essentially unchanged when activated by either the receptormediated agonist (carbachol) or Ca2+ influx (A23187). Thus, these findings implicate a GC-C pathway as a key factor in Caz+-activated mammalian duodenal mucosal bicarbonate secretion.