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

Abstract

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 recordingswere performed in T84 cells using the patch-clamp technique. Berberine decreased forskolininduced short-circuit current in a concentration-dependent manner (IC 50 80±8μM). 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, PKCα and PKA, but had no effect on p42/p44 MAPK and PKCδ. However, berberine pre-treatment prevented stimulation of p42/p44 MAPK by epidermal growth factor. The inhibitory effect of berberine on Cl - secretionwas partially blocked by HBDDE (~65%), an inhibitor of PKCα and to a smaller extent by inhibition of p38 MAPK with SB202190 (~15%). Berberine treatment induced an increase in association between PKCα 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 PKCα-dependent pathway. © 2011 Alzamora, O'Mahony, Ko, Yip, Carter, Irnaten and Harvey.