Activation of ion channels by lysylbradykinin in the HCA-7 colony 29 human adenocarcinoma cell line

Bradykinin regulates human colonic ion transport in vitro

BACKGROUND AND PURPOSE

Kinins are acknowledged as important regulators of intestinal function during inflammation; however, their effects on human intestinal ion transport have not been reported. Here, we used muscle-stripped human colonic tissue and cultured T(84)-cell monolayers to study bradykinin (BK) actions on human intestinal ion transport.

EXPERIMENTAL APPROACH

Ion transport was measured as changes in short-circuit current (I(sc)) across colonic epithelia mounted in Ussing chambers.

KEY RESULTS

In intact tissue, there was a distinct polarity to BK-elicited I(sc) responses. Whereas basolateral BK stimulated sustained responses (EC(50)=0.5+/-0.1 microM), those to apical BK were more rapid and transient (EC(50)=4.1+/-1.2 nM). In T(84) cells, responses to both apical and basolateral BK were similar to those seen upon apical addition to intact tissues. Cross-desensitization between apical and basolateral domains was not observed. BK-induced responses were largely due to Cl(-) secretion as shown by their sensitivity to bumetanide and removal of Cl(-) from the bathing solution. Studies using selective agonists and antagonists indicate responses to BK are mediated by B(2) receptors. Finally, responses to basolateral BK in intact tissues were inhibited by tetrodotoxin (1 microM), atropine (1 microM), capsaicin (100 microM) and piroxicam (10 microM). BK-stimulated prostaglandin (PG)E(2) release from colonic tissue.

CONCLUSIONS

BK stimulates human colonic Cl(-) secretion by activation of apical and basolateral B(2) receptors. Responses to apical BK reflect a direct action on epithelial cells, whereas those to basolateral BK are amplified by stimulation of enteric nerves and PG synthesis.

Kinin-induced chloride permeability changes in colony 29 epithelia estimated from 125I- efflux and MEQ fluorescence

1. The changes in apical Cl- permeability of Colony 29 human colonic epithelial monolayers were estimated from the rate constant of 125I- efflux from tissues loaded with the isotope. 2. Forskolin was used to increase intracellular concentrations of adenosine 3:5' cyclic-monophosphate (cyclic AMP), and A23187 to increase intracellular free Ca2+ (Cai). Both treatments increased the rate constant for 125I- efflux, indicating an increase in apical Cl- permeability. 3. Lysylbradykinin (LBK) also increased the rate constant for 125I- efflux, sometimes biphasically. Chelation of intracellular Ca2+ with BAPTA or prevention of prostaglandin formation with piroxicam, attenuated but did not eliminate the effect of LBK. It is concluded that LBK affects 125I- efflux through the agency of both cyclic AMP and Ca2+. 4. Ba2+ attenuated the effect of LBK and A23187 on 125I- efflux, but had no effect on the action of forskolin. It is concluded that Ca2+ has a major effect on K+ channels, the resulting hyperpolarization increasing the driving force for 125I- efflux. A secondary effect on Ca(2+)-sensitive Cl- channels is possible. By contrast, cyclic AMP exerts it major effect on apical Cl- channels. 5. Using a Cl- sensitive fluorescent dye, MEQ, the intracellular chloride concentration, Cli was estimated to be around 30 mM, which was increased to around 50 mM by forskolin, suggesting cyclic AMP could activate the Na-K-2Cl co-transporter. 6. MEQ fluorescence was used to estimate Cl- influx and efflux rates of epithelial cells. These were increased three fold by forskolin and dibutyryl cyclic AMP and two fold by LBK and histamine. 7. It is concluded that LBK increases electrogenic chloride secretion in Colony 29 epithelia through the generation of second messengers cyclic AMP and Ca2+, each of which may act on both apical and basolateral membranes.

Cyclic AMP and Ca2+ interactions affecting epithelial chloride secretion in human cultured colonic epithelia

1. Chloride secretion in three types of cultured epithelial monolayers derived from a single human colonic adenocarcinoma was measured in terms of short circuit current. The three cell types were designated HCA-7, Colony 3 and Colony 29. 2. Responses of HCA-7 monolayers to basolaterally applied lysylbradykinin (LBK) (10-1000 nM) or carbachol (1-100 microM) were potentiated by pre-exposure to forskolin (10 microM) for 5 min. Forskolin itself increased short circuit current (SCC), so that the total response to forskolin and LBK or carbachol were non-additive. 3. Colony 3 cells did not respond to LBK on either face but did to carbachol on the basolateral side, while Colony 29 epithelia responded to LBK on both sides and to carbachol and histamine basolaterally. Unlike HCA-7 epithelia, responses in Colony 3 and Colony 29 epithelia were not potentiated by forskolin, but were attenuated by piroxicam. 4. In the presence of piroxicam, both forskolin and prostaglandin E2 were able to potentiate the action of both LBK and carbachol in Colony 29 epithelia. 5. LBK receptor activation in Colony 29 epithelia is transduced into an increase in intracellular Ca2+ and cyclic AMP, while in HCA-7 epithelia there is only an increase in intracellular Ca2+ (Cai). These conclusions are considered to apply to both apical and basolateral kinin receptors. 6. It is shown that forskolin has no effect on the elevation of Ca2+ by LBK in either HCA-7 or Colony 29 cells. 7. It is concluded that potentiation of agonist responses occurs when cyclic AMP is raised at the time that intracellular Ca2+ increases. No potentiation of LBK or carbachol by forskolin occurs in Colony 29 monolayers as these agonists increase cyclic AMP via eicosanoid production.