Single chloride channels in colon mucosa and isolated colonic enterocytes of the rat

Abstract

Chloride channels from rat colonic enterocytes were studied using the patch-clamp technique. After removal of mucus, inside-out patches were excised from the apical membrane of intact epithelium located at the luminal surface. They contained spontaneously switching Cl- channels with a conductance of 35-40 pS. The channels were blocked reversibly by anthracene-9-carboxylic acid (1mM). In excised patches from single enterocytes, isolated by calcium removal, the Cl- channels were studied in more detail. The I-V relation was linear between +/- 80 mV. The selectivity was I- greater than Br- greater than Cl- = NO3- greater than F- = HCO3-. Thirty pS Cl- channels were also found on the basolateral membrane of crypts isolated by brief calcium removal. The I-V curve of these Cl- channels was also linear. The results provide direct evidence for the existence of Cl- channels in the apical membrane of surface cells in colonic mucosa. The properties of these channels are similar to those previously observed when incorporating membrane vesicles into planar lipid bilayers. Both results support the validity of the theoretical models describing intestinal secretion.

Extracellular pH regulation in microdomains of colonic crypts: effects of short-chain fatty acids.

“…Most important, we have not defined the epithelial cell types exposed to the pH microdomains. The colonic crypt contains multiple epithelial cell types (1), but sites of ion absorptive and secretory functions along the crypt-to-surface axis are still being established (33)(34)(35). We speculate that extracellular pH regulation could contribute to several recognized effects of SCFAs on colonic ion transport.…”

Thromboxane A2, released by the anti‐ tumour drug irinotecan, is a novel stimulator of Cl− secretion in isolated rat colon

“…Crypts were isolated from the distal colon as previously described (Diener, Rummel, Mestres & Lindemann, 1989). The mucosasubmucosa preparation was fixed on a plastic holder with tissue adhesive and incubated in EDTA solution for 7 min.…”

A chloride channel from lobster walking leg nerves. Characterization of single-channel properties in planar bilayers.

“…However, there are several examples of SC1 channels that do appear to exhibit nearly perfect anion selectivity, as demonstrated by measured PN~.K/Pct ratios of --<0.05. Such examples include the rat colon epithelial SC1 channel (Halm et al, 1988;Diener et al, 1989) and a 40-50-pS channel in the apical membrane of dogfish rectal gland (Greger et al, 1987). The lobster CI-channel described here is also unique in exhibiting a high I-/F-selectivity as measured by the bi-ionic (PI/Po)/(PF/P cl) ratio, which is ~55 in our case (Table I).…”

“…The lobster CI-channel described here is also unique in exhibiting a high I-/F-selectivity as measured by the bi-ionic (PI/Po)/(PF/P cl) ratio, which is ~55 in our case (Table I). Other SC1 channels from neural and secretory cells generally exhibit values of 2.8-4.8 for this parameter (Franciolini and Nonner, 1987;Reinhardt et al, 1987;Halm et al, 1988;Diener et al, 1989).…”