Differential segment-specific signalling pathways for guanylate cyclase C-activated anion secretion in murine...

Guanylate cyclase-C (GC-C) is the receptor for endogenous (uro)guanylin peptides, bacterial toxins and pharmacological analogues. Receptor activation leads to intestinal fluid loss, but also activates an antiproliferative pathway and is a promising target in colorectal cancer therapy. The present study delineates the molecular mechanisms that regulate the intensity of the anion secretory response (ASR) to GC-C activation in the different segments of the murine ileocolon.

To assess the ASR to the guanylin analogue linaclotide, isolated mucosa from the different segments of the ileocolon of cGMP-dependent kinase II (cGKII)-deficient and WT mice were studied electrophysiologically in Ussing-chambers. The mucosal expression pattern of different phosphodiesterases (PDEs) was measured by RT-PCR.

The ASR to linaclotide and 8-pCPT-cGMP was strongly dependent on the presence of cGKII in the ileum and proximal colon, but not in the mid and distal colon, where cGKII expression is low. The inhibition of cGMP-sensitive PDE3 completely prevented the linaclotide-induced ASR only in the mid and distal colon, demonstrating that GC-C dependent ASR occurs via an increase in cAMP in these segments, mediated by the cGMP-induced inhibition of PDE3. In addition, the cGMP-specific PDE9 was highly expressed in the distal colon, and its inhibition strongly enhanced the ASR to linaclotide.

GC-C activation leads to CFTR-mediated ASR in all segments of the intestine. In the mid and distal colon ASR is strongly reduced by the low cGKII and high PDE9 expression, with the CFTR channel being activated via cAMP-mediated phosphorylation.