From each animal, three flat sheets of unstripped ileum free of Peyer’s patches were placed in

Teflon holders and mounted in Ussing chambers within 5 min after being cut off from blood supply. Both sides of the sample (exposed area 0·2 cm2) were in contact with 1·6 mL Krebs–Ringer solution, stirred and gassed with humidified 95% O2 + 5% CO2 at 37°C. The transepithelial potential difference Vte MK0683 mouse (mV) was continuously monitored with Calomel electrodes connected to the chambers with Krebs–Ringer-agar bridges. Transepithelial electrical resistance R (Ω/cm2) was calculated from the voltage deflections induced by bipolar current pulses of 10 μA (every 30 s) applied through platinum wires. The potential and resistance data were stored on a PC using custom software (Natural Simstrument, Amsterdam, the Netherlands). During off-line data analysis, corrections were made for resistance of the solution and for potential differences between Calomel electrodes, measured both just before and immediately

after each experiment. The equivalent short-circuit Ku-0059436 chemical structure current Isc (μA/cm2) was calculated from the continuously monitored values of R and Vte. Reported values for the parameters Vte, R and Isc were obtained at the end of a 15- to 20-min equilibration period. Generally, these values were stable during the subsequent 1- or 2-h experiment. At the end of the experiment, the secretory capacity of the tissue segments was tested by measuring their response (Vte and Isc) to application of the secretagogue carbachol in the serosal compartment (10−4 M). In the Ussing chamber experiments, the measured transepithelial potential

(Vte) and equivalent short-circuit current (Isc) are indicative of the basal epithelial secretion, while the increase in these parameters (dVte and dIsc) in response to the secretagogue carbachol reflects the maximal secretory capacity. Paracellular mucosal-to-serosal permeability was determined using NaFl Casein kinase 1 as a model molecule (25). After the equilibration period, NaFl was added to the mucosal compartment (0·01 g/L) and 200-μL serosal samples were taken every 7·5 min and replaced by Krebs–Ringer. The concentration of NaFl was determined using a fluorimeter (Polarstar Galaxy fluorescence multi-well plate reader; BMG LabTech GmbH, Jena, Germany), with 485 nm and 530 nm as excitation and emission wavelengths respectively. Steady-state NaFl-flux was quantified and expressed as ng/cm2/h. For each animal, average values of electrophysiological parameters and NaFl-flux were calculated from simultaneous measurements of three ileal samples. Statistical analyses were performed using SPSS v.12·0 software (SPSS Inc., Chicago, IL, USA).