Berberine reduces cAMP-induced chloride secretion in T84 human colonic carcinoma cells through inhibition of basolateral KCNQ1 channels

Berberine is a plant alkaloid with multiple pharmacological actions, including antidiarrhoeal activity and has been shown to inhibit Cl secretion in distal colon. The aims of this study were to determine the molecular signaling mechanisms of action of berberine on Cl secretion and the ion transporter targets. Monolayers of T84 human colonic carcinoma cells grown in permeable supports were placed in Ussing chambers and short-circuit current measured in response to secretagogues and berberine. Whole-cell current recordings were performed in T84 cells using the patch-clamp technique. Berberine decreased forskolininduced short-circuit current in a concentration-dependent manner (IC50 80 +/- 8 mu M). In apically permeabilized monolayers and whole-cell current recordings, berberine inhibited a cAMP-dependent and chromanol 293B-sensitive basolateral membrane K+ current by 88%, suggesting inhibition of KCNQ1 K+ channels. Berberine did not affect either apical Cl- conductance or basolateral Na+-K+-ATPase activity. Berberine stimulated p38 MAPK, PKC alpha and PKA, but had no effect on p42/p44 MAPK and PKC delta. However, berberine pre-treatment prevented stimulation of p42/p44 MAPK by epidermal growth factor. The inhibitory effect of berberine on Cl- secretion was partially blocked by HBDDE (similar to 65%), an inhibitor of PKC alpha and to a smaller extent by inhibition of p38 MAPK with SB202190 (similar to 15%). Berberine treatment induced an increase in association between PKC alpha and PKA with KCNQ1 and produced phosphorylation of the channel. We conclude that berberine exerts its inhibitory effect on colonic Cl- secretion through inhibition of basolateral KCNQ1 channels responsible for K+ recycling via a PKC alpha-dependent pathway.