Interleukin-6 modulates colonic transepithelial ion transport in the stress-sensitive wistar kyoto rat

Abstract

Immunological challenge stimulates secretion of the pro-inflammatory cytokine interleukin (IL)-6, resulting in variety of biological responses. In the gastrointestinal tract, IL-6 modulates the excitability of submucosal neurons and stimulates secretion into the colonic lumen. When considered in the context of the functional bowel disorder, irritable bowel syndrome (IBS), where plasma levels of IL-6 are elevated, this may reflect an important molecular mechanism contributing to symptom flares, particularly in the diarrhea-predominant phenotype. In these studies, colonic ion transport, an indicator of absorption and secretion, was assessed in the stress-sensitive Wistar Kyoto (WKY) rat model of IBS. Mucosa-submucosal colonic preparations from WKY and control Sprague Dawley (SD) rats were mounted in Ussing chambers and the basal short circuit current (I(SC)) was electrophysiologically recorded and compared between the strains. Exposure to IL-6 (1 nM) stimulated a secretory current of greater amplitude in WKY as compared to SD samples. Furthermore, the observed IL-6-mediated potentiation of secretory currents evoked by veratridine and capsaicin in SD rats was blunted in WKY rats. Exposure to IL-6 also stimulated an increase in transepithelial resistance in both SD and WKY colonic tissue. These studies demonstrate that the neuroexcitatory effects of IL-6 on submucosal plexi have functional consequences with alterations in both colonic secretory activity and permeability. The IL-6-induced increase in colonic secretory activity appears to neurally mediated. Thus, local increases in IL-6 levels and subsequent activation of enteric neurons may underlie alterations in absorpto-secretory function in the WKY model of IBS.

Keywords: Wistar Kyoto; capsaicin; electrophysiology; interleukin-6; irritable bowel syndrome; ussing chambers; veratridine.

Figure 1

IL-6 modulates transepithelial current and resistance. (A) The histograms illustrates basal short circuit current (I_SC, μA cm², SD: n = 18, WKY: n = 9) and (B) transepithelial resistance (TER, Ω cm², SD: n = 17, WKY: n = 8) in distal colon segments from naïve Sprague Dawley (SD) and Wistar Kyoto (WKY) rats. (C) The histograms and representative trace shows the effect of basolaterally applied IL-6 (1 nM, measured 10 min after application) on basal I_SC (SD: n = 23, WKY: n = 9). (D) This histogram illustrates the change (Δ) in tissue resistance over the course of the experiment (60–90 min, SD: n = 18, WKY: n = 6). Values = mean ± SEM.* Indicates p < 0.05.

Figure 2

Veratridine-induced currents in Sprague Dawley (SD) and Wistar Kyoto (WKY) colons. (A) Representative traces illustrate the secretory current (I_SC) induced by exposure to veratridine (10 μM) in non-stimulated (con) SD (thin gray line, n = 7) and WKY (thin black line, n = 9) colonic sections and IL-6-stimulated SD (thick gray line, n = 7) and WKY (thick black line, n = 9) colonic sections. (B) The histogram shows the pooled data. Values = mean ± SEM. * Indicates p < 0.05.

Figure 3

Cholinergically driven currents in Sprague Dawley (SD) and Wistar Kyoto (WKY) rats are altered by IL-6 exposure. (A) The representative traces show bethanechol-induced increases in short circuit current (I_SC) in control (Con, thin gray line, n = 12) and IL-6-(1 nM) stimulated (IL-6, thick gray line, n = 12) SD colonic tissue. WKY traces are also included for control (thin black line, n = 9) and Il-6-stimulated (thick black line, n = 9) colonic tissues. (B) Histograms show the pooled data. Values = mean ± SEM. * Indicates p < 0.05.

Figure 4

IL-6 alters capsaicin-induced currents in Sprague Dawley (SD) and Wistar Kyoto (WKY) rat colons. (A) The representative traces illustrate the secretory (phase I) and anti-secretory (phase II) responses to capsaicin (1 μM) in control SD (gray line, n = 10) and WKY (black line, n = 10) distal colons. (B) The histogram illustrates the pooled data for changes in current (I_SC). (C) The traces are representative of capsaicin-evoked responses following exposure to IL-6 (1 nM) in SD (n = 11) and WKY (n = 7). (D) The pooled data are plotted in a histogram. Values = mean ± SEM. * indicates p < 0.05.