Localization of chloride secretion in rabbit colon: inhibition by anthracene-9-carboxylic acid

The effect of secretagogues on ion conductances of in vitro perfused, isolated rabbit colonic crypts

Several secretagogues were used in this study, including those which enhance intracellular cyclic adenosine monophosphate (cAMP) production, as well as others which elevate intracellular Ca2+ activity and are known to increase Cl- secretion in the intact colon and in colonic carcinoma cell lines. They were examined with respect to their effects on electrophysiological properties in isolated rabbit distal colonic crypts. Crypts were dissected manually and perfused in vitro. Transepithelial voltage (Vte), transepithelial resistance (Rte), membrane voltage across the basolateral membrane (Vbl), and fractional basolateral membrane resistance (FRbl), were estimated. Basolateral prostaglandin E2 (PGE2, > or = 0.1 mumol/l), vasoactive intestinal peptide (VIP, 1 nmol/l) and adenosine (0.1 mmol/l) induced an initial depolarisation and a secondary partial repolarisation of Vbl. In the case of adenosine, the initial depolarization of Vbl was by 31 +/- 2 mV (n = 47). Rte fell significantly from 16.4 +/- 3.6 to 14.2 +/- 3.7 omega.cm2 (n = 6), and FRbl increased significantly from 0.11 +/- 0.02 to 0.51 +/- 0.10 (n = 6). In the second phase the repolarisation of Vbl amounted 11 +/- 2 mV (n = 47) and a steady-state (Vbl) of -51 +/- 2 mV (n = 47) was reached. Rte fell further and significantly to a steady-state value of 12.4 +/- 3.8 omega.cm2 (n = 6) and FRbl fell significantly to 0.42 +/- 0.13 (n = 6). In 30% of the experiments, a transient hyperpolarisation of Vbl by 8 +/- 2 mV (n = 14) was seen during wash out of adenosine.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence from fluorescence microscopy and comparative studies that rat, ovine and bovine colonic crypts are absorptive

1. To test whether colonic crypts are secretory or absorptive interstitial [Na+] in rat descending colonic mucosa is determined using video-enhanced imaging of the impermeant acid form of the fluorescent Na+ probe SBFI (Molecular Probes) and intracellular [Na+] is monitored with SBFI (AM form). In rat descending colonic mucosa perifused with isotonic Tyrode solution interstitial [Na+] = 500-650 mM. Following exposure to Tyrode solution containing theophylline (10 mM) interstitial [Na+] falls by 300-450 mM within 1 min. Exposure to amiloride (0.2 mM) reduces the intracellular [Na+] from ca 25 to 12 mM within 15 min and concurrently decreases [Na+] in the interstitial fluid surrounding the crypts at the mucosal surface by approximately 200 mM. 2. The route of fluid inflow across the rat colonic mucosa is directly traced by perifusing with Tyrode solution containing the impermeant fluorescent dye, fluorescein disulphonate (FS). FS accumulates rapidly within crypt lumens of control tissues to a 2-fold higher concentration than in the external bathing solution, but FS does not accumulate in crypts of tissues treated with azide (2 mM). The increment in FS accumulation within the crypt lumen above the bulk solution decreases by 80% within 1 min following exposure to theophylline (10 mM), indicating that fluid absorption into crypts is reduced. Estimates of the total fluid influx from the rate and extent of FS concentration polarization within crypts indicate that it is sufficient to account for the entire transcolonic fluid absorption. 3. Comparative studies of isolated bovine and ovine colon were also undertaken to investigate the failure of bovine colon to generate a hypertonic absorbate and hence its incapacity to produce hard faeces. The interstitial fluid surrounding ovine colonic crypts is hypertonic to the bulk solution, whereas the interstitial fluid surrounding bovine colonic crypts is nearly isotonic with the bathing solution. Additionally, fluorescein disulphonate accumulates within ovine colonic crypt lumens by concentration polarization, whereas no concentration of FS occurs within bovine colonic crypt lumens. This corroborates the view that a hypertonic interstitial fluid is absent from bovine colon mainly because of a high rate of transepithelial leakage of low molecular weight solutes via paracellular routes.

Membrane distribution of sodium-hydrogen and chloride-bicarbonate exchangers in crypt and villus cell membranes from rabbit ileum

Present evidence suggests that in the small intestine, villus cells are primarily absorptive and crypt cells are primarily secretory. In order to further confirm that there are differences in transport properties between villus and crypt cells, we have separated villus from crypt cells, using calcium chelations techniques, and determined the distribution of Na:H and Cl:HCO3 exchange activity on brush border membrane and basolateral membrane preparations from these two cell populations. Separation of cells was determined utilizing alkaline phosphatase and maltase activity as a marker of villus cells and thymidine kinase activity as a marker of crypt cells. Utilizing these techniques, we were able to sequentially collect cells along the villus-crypt axis. Na-stimulated glucose and alanine uptake in brush border membrane vesicles diminished from the villus to the crypt region in the sequentially collected cells fractions, further suggesting separation of these cells. Brush border and basolateral membranes were then prepared from cells from the villus and crypt areas, utilizing a continuous sucrose gradient. In the villus cells, Na:H exchange activity was found associated with both the brush border and basolateral membrane, whereas, in crypt cells, Na:H exchange activity was only found on the basolateral membrane. Cl:HCO3 exchange activity was found only on the brush border membrane, in both villus and crypt cells. These studies suggest functional heterogeneity in ion transport between villus and crypt cells.