Independence of the activation of mucus and potassium secretion on the inhibition of sodium and water absorption by deoxycholate in rat colon

Chronic diarrhoea following surgery for colon cancer-frequency, causes and treatment options

PURPOSE

The growing population of survivors after colon cancer warrants increased attention to the long-term outcome of surgical treatment. The change in bowel anatomy after resection disrupts normal gastrointestinal function and may cause symptoms. Thus, many patients surviving colon cancer have to cope with bowel dysfunction for the rest of their lives. We here aim to provide an overview of the literature on this topic.

METHODS

We review long-term functional outcomes of surgical treatment for colon cancer, the underlying pathology, and treatment options.

RESULTS

Common symptoms include constipation, urge for defecation and diarrhoea. Causes of diarrhoea after colon cancer surgery are sparsely studied, but they probably include bile acid malabsorption, small intestinal bacterial overgrowth and disruption of the ileal brake. Specific diagnosis should be made to allow individual treatment based on the underlying pathology. Studies on treatment of functional problems after surgery for colon cancer are extremely few, but some lessons can be drawn from the treatment of other patient groups having undergone colon surgery.

CONCLUSION

Diarrhoea is likely a common long-term complication after colon cancer surgery. Attention to this complication and a specific diagnosis will aid the targeted treatment of patients suffering from this complication.

Apical potassium (BK) channels and enhanced potassium secretion in human colon

The human colon has the capacity to secrete potassium (K(+)) ions and enhanced K(+) secretion is a feature of a variety of diarrhoeal diseases. Recent work points to K(+) secretion in human colon being mediated by high conductance (BK) K(+) channels located in the apical membrane of colonic epithelial cells. The aim of this review is to highlight the importance of these channels in maintaining K(+) homoeostasis in health and disease.

Ca2+-dependent K+ efflux regulates deoxycholate-induced apoptosis of BHK-21 and Caco-2 cells

BACKGROUND & AIMS

Deoxycholate (DC) has proapoptotic and tumorigenic effects in different cell types of the gastrointestinal tract. Exposure of BHK-21 (stromal) cells to DC induces Ca(2+) entry at the plasma membrane, which affects intracellular Ca(2+) signaling. We assessed whether DC-induced increases in [Ca(2+)] can impinge on plasma membrane properties (eg, ionic conductances) involved in cell apoptosis.

METHODS

Single- and double-barreled microelectrodes were used to measure membrane potential (V(m)) and extracellular [K(+)] in BHK-21 fibroblasts and Caco-2 colon carcinoma cells. Apoptosis was assessed by Hoechst labeling, propidium iodide staining, and caspase-3 and caspase-7 assays.

RESULTS

DC-induced cell membrane hyperpolarization was directly measured with intracellular microelectrodes in both cell lines. Diverse Ca(2+) mobilizing agents, such as membrane receptor agonists, an inhibitor of the sarco/endoplasmic reticulum Ca(2+) adenosine triphosphatase and a Ca(2+) ionophore, also induced increases in V(m). Removal of extracellular Ca(2+) reduced the agonist- and DC-induced membrane hyperpolarization by approximately 15% and 60%, respectively. These findings indicate a prominent role for Ca(2+) entry at the plasma membrane in the action of this bile salt. Blockade of Ca(2+)-activated K(+) conductances by charybdotoxin and apamin reduced DC-induced hyperpolarization by 75% and 64% in BHK-21 and Caco-2 cells, respectively. These inhibitors also reduced the DC-induced increase in extracellular [K(+)] by 75% and cell apoptosis by approximately 50% in both cell lines.

CONCLUSIONS

Ca(2+)-dependent K(+) conductance is an important regulator of DC-induced apoptosis in stromal and colon cancer cells.

Involvement of enteric nerves in permeability changes due to deoxycholic acid in rat jejunum in vivo

AIM

Stress and Clostridium difficile toxin A increase epithelial permeability in the small intestine via vagus and visceral afferents, in turn activating mucosal mast cells. Bile acids also increase epithelial permeability but it is not known if nerves or mast cells are involved in this effect in the small intestine.

METHOD

In jejunum of anesthetized rats, the effects of hexamethonium and atropine on deoxycholic acid (DCA) induced fluid secretion and increase in epithelial permeability was therefore studied by determining the appearance and disappearance rates of 14C-mannitol and 51Cr-EDTA into and from a perfusion system containing 4 or 8 mm DCA and expressed as clearance.

RESULTS

DCA increased net fluid transport and appearance and to a less extent disappearance rates of the probes. Hexamethonium but not atropine, chronic denervation or the NO synthase inhibitor L-NNA did significantly decrease the appearance rate and net fluid secretion. The levels of the mast cell protease II (RMCP II) in perfusate and plasma were not increased by DCA. The clearance ratio Cr-EDTA/mannitol indicates that the plasma clearance of the permeability probes is partly secondary to net fluid transport only at higher DCA concentrations.

CONCLUSION

We conclude that the DCA effect on epithelial permeability is to a large part induced by intramural reflex(es) containing nicotinic receptors. The results also suggest that mast cell degranulation and NO release are not involved in the mechanism. This indicates that the nerve effect on intestinal paracellular permeability is not mediated by the mechanisms described for stress or Clostridium difficile toxin A.

Effects of nicotinic receptor blockade on the colonic mucosal response to luminal bile acids in anaesthetized rats

AIM

To test the hypothesis that nicotinic receptor mechanisms mediate the effects of bile acids on the colonic mucosa.

METHODS

The epithelial transport response to 4 mm deoxycholic acid (DCA) was studied in vitro and in vivo, in rat colon. In vitro, epithelial resistance was measured by square pulse analysis, and net membrane current was calculated from the transmucosal potential difference (PD) and resistance. In vivo, we measured PD and net fluid transport.

RESULTS

In vitro, DCA significantly increased membrane current and induced a progressive decrease in epithelial resistance, which in the distal colon eventually resulted in a significant PD reduction. This response was not significantly affected by hexamethonium. In vivo, DCA reduced PD with a significantly larger response in distal colon, but had no consistent effect on net fluid absorption. Nicotinic receptor blockade per se increased net fluid absorption and slightly reduced PD in proximal colon, and inhibited spontaneous net fluid secretion and markedly reduced PD in distal colon. Nicotinic receptor blockade significantly attenuated the bile-acid induced PD response.

CONCLUSION

The data do not support the theory that a bile acid-activated secretory reflex exists in rat colon. The reduced PD response after hexamethonium suggests that a mechanism involving nicotinic receptors may potentiate the permeability response to luminal bile acids.

Endogenous endothelin in a rat model of acute colonic mucosal injury

BACKGROUND

Endothelin (ET) is involved in various biologic activities in non-vascular and vascular tissues. While ET has some significant effects on gastrointestinal functions, the possible role of endogenous ET in the host response to mucosal injury has not been well clarified.

METHODS

The present study describes an investigation of the effects of an endothelin A receptor antagonist, BQ-123, on lactate dehydrogenase (LDH), mucus and albumin flux into the perfusate in a rat model of acute colonic injury, induced by acetic acid perfusion. The present study also examined localization of ET in damaged rat colons by using immunohistochemistry.

RESULTS

A 4% acetic acid treatment induced mild mucosal damage of perfused rat colon and increased LDH as well as albumin and protein-bound hexose release into the perfusate. Pretreatment with BQ-123 significantly reduced LDH activity and protein-bound hexose concentration in the perfusate and delayed the reduction of albumin leakage from damaged mucosa. Vascular endothelial, neural and surface epithelial cells of the colon showed strong ET-like immunoreactivity. Mucosal damage markedly influenced ET expression by epithelial cells. Mild mucosal damage decreased the ET expression by surface epithelial cells while moderate mucosal damage induced a mosaic location of ET-positive epithelial cells in the crypt. Severe mucosal damage abolished the ET expression by epithelial cells.

CONCLUSIONS

Endothelin may play a role in the host response to acute mucosal damage. Mucosal ET production is significantly affected by mucosal injury.

Inhibition by loperamide of mucus secretion in the rat colon in vivo

The effect of loperamide on mucus secretion and the net transport of fluid, sodium and potassium was investigated in the perfused rat colon in vivo. Prostaglandin E2 (PGE2, 1 mg/kg per h intraarterially) and deoxycholic acid (2 mM intraluminally) were used as secretagogues. Mucus secretion was determined as the total amount of protein-bound hexose in the effluent. Under basal conditions, loperamide (6 mg/kg subcutaneously) slightly decreased mucus secretion and increased the absorption of fluid and sodium. PGE2 and deoxycholic acid stimulated mucus secretion about 4- and 9-fold, respectively. Loperamide abolished the mucus secretory response to PGE2 and reduced the response to deoxycholic acid by 50%. It also reduced the fluid secretion following PGE2 but did not affect the diminished fluid absorption following deoxycholic acid. Potassium secretion was not significantly influenced by loperamide and therefore was independent of the secretion of mucus. The data suggest that loperamide is a potent inhibitor of colonic mucus secretion, a property that possibly contributes to the antidiarrheal effect of this opiate analogue.

Influence of vasoactive intestinal peptide, secretin, and Ala4, Val5-secretin on the net movements of electrolytes, fluid, and mucus in the rat colon in vivo

The effect of vasoactive intestinal peptide (VIP), secretin, and VIP-secretin (Ala4, Val5-secretin) on the net movements of sodium, potassium, fluid, and mucus was investigated in the rat colon perfused in vivo. Peptides (1-100 micrograms/kg.h) were infused intra-arterially. VIP influenced electrolyte and fluid movements at a threshold dose 10- to 100-fold lower than secretin, whereas the secretory efficacy was not significantly different. Replacing the NH2-terminal hexapeptide of secretin by that of VIP did not markedly alter the effect of secretin. Mucus output was stimulated weakly by all three peptides. The results indicate that the larger colonic secretory activity of VIP as compared to secretin is not primarily due to the difference in their NH2-terminal sequence but probably requires the intact molecule.

The influence of bisacodyl and deacetylbisacodyl on mucus secretion, mucus synthesis and electrolyte movements in the rat colon in vivo

The effect of the diphenolic laxatives bisacodyl and deacetylbisacodyl on mucus secretion and fluid, sodium and potassium net transport was studied in rat colon perfused in vivo. Mucus output in the effluent was determined as total protein-bound hexose. Deacetylbisacodyl was more potent than the parent compound and was used to investigate dose-response relationships. At a low concentration (0.1 mg/dl), mucus and potassium secretion were stimulated whereas sodium and fluid absorption were inhibited, or converted to secretion, only at higher concentrations (0.5-3.0 mg/dl). All effects were dose-dependent and reversible within 1 h. With longer lasting perfusion of deacetylbisacodyl, mucus appeared in two peaks, one initial peak and another after 4 h. The late peak contained newly synthetized glycoproteins as indicated by the incorporation of intravenously injected [14C]galactose. It is concluded that stimulation of mucus secretion and synthesis contributes to the laxative action of bisacodyl. The effects of low versus high concentrations suggests that part of the potassium secretion is due to mucus release.