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en: Involvement of butyrate in electrogenic K+ secretion in rat rectal colon.

en: Short-chain fatty acids (SCFAs), such as acetate, propionate, and butyrate, are synthesized from dietary carbohydrates by colonic bacterial fermentation. These SCFAs supply energy, suppress cancer, and affect ion transport. However, their roles in ion transport and regulation in the intracellular environment remain unknown. In order to elucidate the roles of SCFAs, we measured short-circuit currents (ISC) and performed RT-PCR and immunohistochemical analyses of ion transporters in rat rectal colon. The application of 30 mM butyrate shifted ISC in a negative direction, but did not attenuate the activity of epithelial Na+ channels (ENaC). The application of bumetanide, a Na+-K+-2Cl- cotransporter inhibitor, to the basolateral side reduced the negative ISC shift induced by butyrate. The application of XE991, a KCNQ-type K+ channel inhibitor, to the apical side decreased the ISC shift induced by butyrate in a dose-dependent manner. The ISC shift was independent of HCO3- and insensitive to ibuprofen, an SMCT1 inhibitor. The mucosa from rat rectal colon expressed mRNAs of H+-coupled monocarboxylate transporters (MCT1, MCT4, and MCT5, also referred to as SLC16A1, SLC16A3, and SLC16A4, respectively). RT-PCR and immunofluorescence analyses demonstrated that KCNQ2 and KCNQ4 localized to the apical membrane of surface cells in rat rectal colon. These results indicate that butyrate, which may be transported by H+-coupled monocarboxylate transporters, activates K+ secretion through KCNQ-type K+ channels on the apical membrane in rat rectal colon. KCNQ-type K+ channels may play a role in intestinal secretion and defense mechanisms in the gastrointestinal tract.

en: Pflügers Archiv : European Journal of Physiology


en: The adenosine A2B receptor is involved in anion secretion in human pancreatic duct Capan-1 epithelial cells.

en: Adenosine modulates a wide variety of biological processes via adenosine receptors. In the exocrine pancreas, adenosine regulates transepithelial anion secretion in duct cells and is considered to play a role in acini-to-duct signaling. To identify the functional adenosine receptors and Cl(-) channels important for anion secretion, we herein performed experiments on Capan-1, a human pancreatic duct cell line, using open-circuit Ussing chamber and gramicidin-perforated patch-clamp techniques. The luminal addition of adenosine increased the negative transepithelial potential difference (V te) in Capan-1 monolayers with a half-maximal effective concentration value of approximately 10 M, which corresponded to the value obtained on whole-cell Cl(-) currents in Capan-1 single cells. The effects of adenosine on V te, an equivalent short-circuit current (I sc), and whole-cell Cl(-) currents were inhibited by CFTRinh-172, a cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel inhibitor. The adenosine A2B receptor agonist, BAY 60-6583, increased I sc and whole-cell Cl(-) currents through CFTR Cl(-) channels, whereas the A2A receptor agonist, CGS 21680, had negligible effects. The A2B receptor antagonist, PSB 603, inhibited the response of I sc to adenosine. Immunohistochemical analysis showed that the A2A and A2B receptors colocalized with Ezrin in the luminal membranes of Capan-1 monolayers and in rat pancreatic ducts. Adenosine elicited the whole-cell Cl(-) currents in guinea pig duct cells. These results demonstrate that luminal adenosine regulates anion secretion by activating CFTR Cl(-) channels via adenosine A2B receptors on the luminal membranes of Capan-1 cells. The present study endorses that purinergic signaling is important in the regulation of pancreatic secretion.

ja: Pflügers Archiv : European Journal of Physiology


en: Functional characterization of a ClC-2-like Cl(-) conductance in surface epithelial cells of rat rectal colon.

en: ClC-2, a member of the voltage-gated Cl(-) channel family, is expressed in the distal colonic surface epithelial cells of various species, but its functional significance remains unclear. Here, by means of electrophysiological and molecular biological techniques, we have identified and characterized a ClC-2-like conductance naturally expressed by surface epithelial cells acutely dissociated from rectal colon of rats fed a standard diet. Whole-cell patch-clamp experiments showed that the surface cells, whether an amiloride-sensitive Na(+) conductance was present or not, displayed a strong hyperpolarization-activated, inwardly rectifying Cl(-) current. Analysis both by in situ hybridization and immunohistochemistry confirmed the expression of ClC-2 in the rectal surface epithelium. The native Cl(-) current shared common electrophysiological properties including voltage-dependent activation, anion selectivity sequence, and Zn(2+) sensitivity with that recorded from HEK293 cells transfected with ClC-2 cloned from rat rectal colon (rClC-2). Cell-attached patch recordings on the surface cells revealed that native ClC-2-like currents activated only at potentials at least 40 mV more negative than resting membrane potentials. In Ussing chamber experiments with rat rectal mucosa, either basolateral or apical application of Zn(2+) (0.1 mM), which inhibited both native ClC-2-like currents and recombinant rClC-2 currents, had little, if any, effects on basal amiloride-sensitive short-circuit current. Collectively, these results not only demonstrate that a functional ClC-2-type Cl(-) channel is expressed in rat rectal surface epithelium, but also suggest that the channel activity may be negligible and thus nonessential for controlling electrogenic Na(+) transport in this surface epithelium under basal physiological conditions.

en: The Journal of Membrane Biology

ja: The Journal of Membrane Biology


en: Amiloride-sensitive epithelial Na+ channel currents in surface cells of rat rectal colon.

en: Surface cells of the mammalian distal colon are shown to molecularly express the amiloride-sensitive epithelial Na+ channel composed of three homologous subunits (alpha-, beta-, and gamma-ENaC). However, because basic electrophysiological properties of amiloride-sensitive Na+ channels expressed in these cells are largely unknown at the cellular level, functional evidence for the involvement of the subunits in the native channels is incomplete. Using electrophysiological techniques, we have now characterized functional properties of native ENaC in surface cells of rectal colon (RC) of rats fed a normal Na+ diet. Ussing chamber experiments showed that apical amiloride inhibited a basal short-circuit current in mucosal preparation of RC with an apparent half-inhibition constant (Ki) value of 0.20 microM. RT-PCR analysis confirmed the presence of transcripts of alpha-, beta-, and gamma-rENaC in rectal mucosa. Whole cell patch-clamp experiments in surface cells of intact crypts acutely isolated from rectal mucosa identified an inward cationic current, which was inhibited by amiloride with a Ki value of 0.12 microM at a membrane potential of -64 mV, the inhibition being weakly voltage dependent. Conductance ratios of the currents were Li+ (1.8) > Na+ (1) > K+ ( approximately 0), respectively. Amiloride-sensitive current amplitude was almost the same at 15 or 150 mM extracellular Na+, suggesting a high Na+ affinity for current activation. These results are consistent with the hypothesis that a heterooligomer composed of alpha-, beta-, and gamma-ENaC may be the molecular basis of the native channels, which are responsible for amiloride-sensitive electrogenic Na+ absorption in rat rectal colon.

en: American Journal of Physiology, Cell Physiology