Proceedings of The Physiological Society
Durham University (2010) Proc Physiol Soc 21, PC30
Lack of effect in vivo of K+ channel modulators on jejunal fluid absorption after Escherichia coli toxin (STa) challenge
M. L. Lucas1, L. C. Gilligan1, C. Whitelaw1, P. J. Wynne1, J. D. Morrison1
1. University of Glasgow, Glasgow, United Kingdom.
A prevalent model for diarrhoeal disease (1) envisages enterocyte chloride ion secretion into the lumen, on the assumption that enterocytes work in reverse and secrete as well as absorb. Heat stable STa toxin from E.coli is thought to conform to this model but in vivo loops fail to secrete on exposure to toxin, although inhibited absorption is found (5). A sub-hypothesis of the electrogenic secretion model is that secretion is assisted by enterocyte membrane potential being maintained by K+ channel opening to allow luminal chloride ion exit. The hypothesis that K+ channel blockers, glibenclamide and clotrimazole should restore fluid absorption and cromakalim should worsen fluid absorption inhibited by STa was tested in vivo in rat jejunum. Fluid uptake was measured (2) in anaesthetised (70 mg/kg i.p Sagatal) unfasted Sprague-Dawley female rats using recovered volume. Twenty five loops were perfused with 100 mM NaHCO3/54 mM NaCl, with 80 ng/ml E. coli STa, with or without 300 uM glibenclamide, 50 uM clotrimazole or 2 uM cromakalim intraluminally or 30 mg/Kg i.v. glibenclamide, 50 mg/Kg i.v. clotrimazole or 5 ug/Kg i.v. cromakalim. After experiment, animals were humanely killed. Results are given as the mean fluid absorption (ul/cm/hr) with standard error of the mean, plus number of animals. One loop was used per experiment. Significance was by ‘t’ test, correcting for multiple comparisons. Net fluid absorption was 98.8 ± 8.8 (9) ul/cm/hr in control perfused jejunal loops and was 38.5 ± 4.2 (8) ul/cm/hr in loops perfused with STa. Co-perfusion with 300 uM glibenclamide or with 50 uM clotrimazole, concentrations identified (3) as inhibiting STa mediated elevations in short-circuit current and proposed as anti-secretory compounds, had no effect on STa inhibited fluid absorption when measured in vivo. The K+ channel opener also did not alter inhibited fluid absorption although identified as anti-secretory (4). Intravenous perfusion was also without effect on fluid absorption inhibited by STa, although anticipated vasomotor effects namely hypotension in the cases of clotrimazole and cromakalim and a mild pressor effect with glibenclamide were found. Our findings are that K+ channel regulators are unable to affect fluid absorption that has been inhibited by E.coli STa. These experiments challenge a further aspect of the dogma of enterocyte chloride ion secretion being the basis for the diarrhoeal disease when the intestine is exposed to STa.
Where applicable, experiments conform with Society ethical requirements