Research Paper
Subject Category: Gastrointestinal pharmacology
British Journal of Pharmacology (2008) 153, 1203–1213; doi:10.1038/sj.bjp.0707684; published online 21 January 2008
Palmatine, a protoberberine alkaloid, inhibits both Ca2+- and cAMP-activated Cl- secretion in isolated rat distal colon
D Z Wu1,2, J Y Yuan1, H L Shi1 and Z B Hu1
- 1Laboratory of Pharmacology, Institute of Chinese Materia Medica, Shanghai University of TCM, Shanghai, PR China
- 2E-Institute of TCM Internal Medicine, Shanghai Municipal Education Commission, Shanghai, PR China
Correspondence: Professor ZB Hu, Institute of Chinese Materia Medica, Shanghai University of Traditional Chinese Medicine, 1200 Cailun Road, Zhangjiang Hi-tech Park, Shanghai 201203, PR China. E-mail: zhibihu@hotmail.com
Received 20 August 2007; Revised 18 October 2007; Accepted 23 November 2007; Published online 21 January 2008.
Abstract
Background and purpose:
The protoberberine alkaloid berberine has been reported to inhibit colonic Cl- secretion. However, it is not known if other protoberberine alkaloids share these effects. We have therefore selected another protoberberine alkaloid, palmatine, to assess its effects on active ion transport across rat colonic epithelium.
Experimental approach:
Rat colonic mucosa was mounted in Ussing chambers and short circuit current (I SC), apical Cl- current and basolateral K+ current were recorded. Intracellular cAMP content was determined by an enzyme immunoassay. Intracellular Ca2+ concentration was measured with Fura-2 AM.
Key results:
Palmatine inhibited carbachol-induced Ca2+-activated Cl- secretion and the carbachol-induced increase of intracellular Ca2+ concentration. Palmatine also inhibited cAMP-activated Cl- secretion induced by prostaglandin E2 (PGE2) or forskolin. Palmatine prevented the elevation of intracellular cAMP by forskolin. Determination of apical Cl- currents showed that palmatine suppressed the forskolin-stimulated, apical cAMP-activated Cl- current but not the carbachol-stimulated apical Ca2+-activated Cl- current. Following permeabilization of apical membranes with nystatin, we found that palmatine inhibited a carbachol-stimulated basolateral K+ current that was sensitive to charybdotoxin and resistant to chromanol 293B. However, the forskolin-stimulated basolateral K+ current inhibited by palmatine was specifically blocked by chromanol 293B and not by charybdotoxin.
Conclusions and implications:
Palmatine attenuated Ca2+-activated Cl- secretion through inhibiting basolateral charybdotoxin-sensitive, SK4 K+ channels, whereas it inhibited cAMP-activated Cl- secretion by inhibiting apical CFTR Cl- channels and basolateral chromanol 293B-sensitive, KvLQT1 K+ channels.
Keywords:
chloride secretion, colonic mucosa, palmatine, short circuit current, ion currents, cyclic adenosine monophosphate, intracellular calcium concentration
Abbreviations:
293B, chromanol 293B; 8-bromo-cAMP, 8-bromoadenosine 3',5'-cyclic monophosphate; [Ca2+]i, intracellular Ca2+ concentration; CFTR, cystic fibrosis transmembrane conductance regulator; ChTX, charybdotoxin; CLT, clotrimazole; DIDS, 4,4'-diisothiocyanato-stilbene-2,2'-disulphonic acid; DMSO, dimethylsulphoxide; IBMX, isobutylmethylxanthine; ISC, short circuit current; KvLQT1 (KCNQ1), voltage-dependent delayed activated K+ channel; NPPB, 5-nitro-2-(3-phenylpropylamino)-benzoic acid; PGE2, prostaglandin E2; SITS, 4-acetamido-4'-isothiocyanato-stilbene-2,2'-disulphonic acid; SK4, small-conductance Ca2+-activated K+ channel
