The Secretory Response of the Rat Colon to the Flavonol Quercetin is Dependent on Ca²⁺‐Calmodulin

Abstract

The dietary flavonol quercetin induces chloride secretion in rat intestine. To clarify the underlying mechanisms, experiments were performed in Ussing chambers with tissue from rat proximal and distal colon. Quercetin induced an increase in short‐circuit current (Isc), which was largely independent of submucosal neurons, as it was not affected by the neurotoxin tetrodotoxin. The effect of quercetin was blocked by the calmodulin antagonists trifluoperazine and ophiobolin A and was diminished by a blocker of Ca2+ release from intracellular stores (TMB‐8), whereas the muscarinic receptor antagonist atropine was ineffective. The quercetin‐induced Isc was abolished in Ca2+‐free solution. The flavonol was able to further increase Isc after maximal stimulation of the cAMP pathway by forskolin. The Isc increase by the flavonol was differently affected by two analogous phosphodiesterase inhibitors. Whereas 3‐isobutyl‐1‐methylxanthine (IBMX) antagonized the effect of quercetin, 8‐methoxymethyl‐IBMX had no effect. Both phosphodiesterase inhibitors similarly influenced the Isc increase induced by forskolin. These results indicate that the chloride secretion induced by quercetin in rat colon depends on Ca2+ and calmodulin. The cAMP pathway and inhibition of phosphodiesterase appear not to be responsible for the secretory activity of the flavonol.

The flavonol quercetin activates basolateral K+ channels in rat distal colon epithelium

“…Quercetin increased I sc in intact distal colon tissue sheets bathed in buffer solution as previously demonstrated (Cermak et al ., 1998; 2000). A first set of experiments was carried out in order to identify the apical Cl − channels involved.…”

“…In contrast to intact colon mucosa, both blockers failed to significantly alter the quercetin‐induced current (Figure 7b). In a previous study, we showed that Gd 3+ , a lanthanide which is able to inhibit the carbachol‐induced Ca 2+ influx into colon mucosa (Frings et al ., 1999), had no effect on the short‐circuit current induced by quercetin (Cermak et al ., 2000). In distal colon epithelium permeabilized with nystatin, the serosal addition of Gd 3+ (100 μ M ) affected neither basal I K nor the current induced by the flavonol (Figure 7a,b).…”

“…At first sight, these results seem to be contrary to our previous studies in which we could clearly demonstrate that the secretion evoked by quercetin is independent of cyclic AMP, but dependent on Ca 2+ (Cermak et al ., 1998; 2000). One possible explanation is that quercetin acts on KCNQ1, which might also be activated by Ca 2+ other than cyclic AMP (Warth et al ., 1999).…”

“…Quercetin diminishes the secretion evoked by the muscarinic agonist carbachol. However, we demonstrated that the flavonol does not act via muscarinic receptors (Cermak et al ., 1998; 2000). Since quercetin's activity is dependent on Ca 2+ , the flavonol should activate basolateral K + channels in a similar manner to carbachol.…”

Basolateral Ca2+‐dependent K+‐channels play a key role in Cl—secretion induced by taurodeoxycholate from colon mucosa

“…Here we show that clotrimazole, an rSK4 channel blocker (Devor et al, 1997), completely inhibited TDC-induced increase in I SC . At variance with TDC-induced Ca 2+ influx (Dharmsathaphorn et al, 1989), quercetin increases intracellular Ca 2+ concentration by mobilization from deposits (Cermak et al, 2000). Indeed, the prosecretory effect of quercetin persisted in the Ca 2+ -free buffer (which was not the case for TDC).…”