Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA111

Poster Communications

Relative contribution of inhibition of sodium-hydrogen exchanger 3( NHE3)-mediated fluid absorption and cystic fibrosis transmembrane conductance regulator( CFTR)-mediated fluid secretion to the increase in intraluminal alkalinity and fluidity induced by the heat-stable Escherichia coli enterotoxin (STa) analogue linaclotide

Q. Tan1, G. di Stefano1, J. Qian1,2, D. Römermann1, A. Majumder1, B. Riederer1, U. E. Seidler1

1. Gastroenterology, Hannover Medical School, Hannover, Germany. 2. Gastrointestinal Surgery, Zhejiang University, Hangzhou, China.

Background: Constipation and intestinal obstructive episodes are major health problems in cystic fibrosis patients. The heat-stable Escherichia coli enterotoxin STa, the endogenous analogues guanylin and uroguanylin and the synthetic analogues linaclotide and plecatanide induce an increase in gut fluidity via binding to the guanylate cyclase C and eliciting cGMP and possibly cAMP production in the enterocyte. This results in stimulation of CFTR-mediated anion secretion and inhibition of NHE3-mediated fluid absorption. Theoretically, the effect of STa/guanylin/linaclotide on NHE3 inhibition may be preserved in the CF gut, but this has not been studied. Aim: We investigated whether and how well the STa analogue linaclotide inhibits fluid absorption and increases alkaline secretion in the jejunum of CFTR null (CFTR KO), F508del mutant, and WT mice in vivo. Methods and Results: 10-7M of the STa analogue linaclotide was added to the jejunal perfusate during single pass perfusion of a jejunal segment in isoflurane-anesthetized(5% for induction, 1,8-2,2% for maintaining), acid/base- and blood pressure controlled CFTR KO, F508del mutant, and WT mice. Net fluid balance before and after linaclotide application was assessed gravimetrically, and the net alkaline output into the perfusate was determined by pH-stat backtitration. Basal fluid absorptive rate was significantly higher in CFTR KO and F508del mutant than in WT mice (147±33, 148±34, and 140±24 µl/cm/h at 10 min (t10), 20 (t20) and 30 (t30) min after stabilization in CFTR KO, 130±26, 126± 23, and 130 ±19 µl/cm/h at t10, 20 and 30 in F508del, and 113 ±20, 114 ±21, 114 ±21 µl/cm/h at t10, 20 and 30 in the WT jejunum. Basal HCO3- output was 3,6 ±1,4 µeq/cm/h in WT, 1,7±0.7 in F508del, and 1,28±0,4 in CFTR KO jejunum. 10-7M linaclotide resulted in a change from jejunal fluid absorption to secretion by 178±28 µl/cm/h in WT, by 70±18 µl/cm/h in CFTR KO and by 58±20 µl/cm/h in F508del jejunum, while it increased HCO3- output by 5,6±1,3 µeq/cm/h in WT, by 3,1±1.1 in F508del, and by 1,7±0,6 in CFTR KO jejunum (n=5-7). Summary and conclusions: The results demonstrate that activating the GCC receptor elicits a decrease in jejunal fluid absorption and an increase in luminal alkalinity in CFTR KO and F508del mutant mice. Targeting this pathway pharmacologically may be an effective method to improve gut fluidity and alkalinity in CF patients.

Where applicable, experiments conform with Society ethical requirements