Anion and fluid secretory response of the murine jejunum to the heat‐stable Eschericia coli enterotoxin (STa) analogue linaclotide: Involvement of NHE3, Slc26a6, CFTR, proteinkinase GII (cGKII) and NHERF1‐3.

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The different PDZ‐adaptors of the NHERF family differentially associate with intestinal electrolyte transporters and modulate their activity in an agonist‐specific fashion. STa induces secretory diarrhea via binding to the guanylate cyclase C, eliciting cGMP production, resulting both in a stimulation of CFTR‐mediated anion secretion and an inhibition of NHE3‐mediated fluid absorption, and these effects are modulated by different NHERF adaptor proteins in cell lines.AimWe studied the STa‐mediated short circuit current response in isolated jejunal mucosa as well as the STa action on in vivo fluid transport in anethstized mice, deficiet for NHE3, Slc26a6, CFTR and NHERF1‐3, to study how well in vitro and in vivo modulation of fluid transport by the above named transporters and NHERF proteins may correlate.Results10−7M of the STa analogue linacolide was applied to the luminal bath of chambered isolated jejunal mucosa of CFTR‐, NHE3‐, Slc26a6‐, cGKII, and NHERF1–3 deficient and WT mice, and short circuit current (Isc) response was measured. The same concentration of linaclotide was added to the jejunal perfusate during single pass perfusion of a jejunal segment in isoflurane‐anesthetized, acid/base‐ and blood pressure controlled KO and WT mice, and net fluid balance before and after linaclotide application assessed gravimetrically. The peak Isc response to linaclotide in chambered jejunal mucosa was absent in CFTR KO, reduced by 88% in cGKII KO, by 40% in NHERF1 KO, and not significantly in NHERF2, NHERF (PDZK1) and SLC26a6 KO isolated jejunal mucosa. In contrast, the magnitude of change from jejunal fluid absorption to secretion in vivo was reduced by 51% in cGKII KO, 49% in CFTR KO, 45% in NHERF1 KO, by 34% in NHERF2 KO, and not significantly in NHERF3 KO and Slc26a6 KO anesthetized mice. NHE3 deletion (48%), pharmacological NHE3 inhibition (50%) or Slc26a6 deletion (44%) also reduced the STa‐elicited change in fluid movement.ConclusionsThe results demonstrate that Isc measurements in isolated small intestinal mucosa are excellent models to selectively study agonist‐mediated CFTR activation, but do not accurately predict in vivo “secretory responses”, i.e. a relative decrease in the basal fluid absorptive flux. Activating the GCC receptor elicited a decrease in fluid absorption in CFTR KO mice, making this substance an interesting drug to improve gut fluidity in CF patients. Apart from direct interference with guanylate cyclase C activation, potential pharmacological strategies to prevent STa‐mediated fluid loss may be targeting both NHERF1 and NHERF2.Support or Funding InformationFunded by SFB621/C1, DFG grants SE460/13‐4, 19‐1 and 21‐1.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.