Cloning and Function of the Rat Colonic Epithelial K + Channel K V LQT1

Abstract

KVLQT1 (KCNQ1) is a voltage-gated K+ channel essential for repolarization of the heart action potential that is defective in cardiac arrhythmia. The channel is inhibited by the chromanol 293B, a compound that blocks cAMP-dependent electrolyte secretion in rat and human colon, therefore suggesting expression of a similar type of K+ channel in the colonic epithelium. We now report cloning and expression of KVLQT1 from rat colon. Overlapping clones identified by cDNA-library screening were combined to a full length cDNA that shares high sequence homology to KVLQT1 cloned from other species. RT-PCR analysis of rat colonic musoca demonstrated expression of KVLQT1 in crypt cells and surface epithelium. Expression of rKVLQT1 in Xenopus oocytes induced a typical delayed activated K+ current, that was further activated by increase of intracellular cAMP but not Ca2+ and that was blocked by the chromanol 293B. The same compound blocked a basolateral cAMP-activated K+ conductance in the colonic mucosal epithelium and inhibited whole cell K+ currents in patch-clamp experiments on isolated colonic crypts. We conclude that KVLQT1 is forming an important component of the basolateral cAMP-activated K+ conductance in the colonic epithelium and plays a crucial role in diseases like secretory diarrhea and cystic fibrosis.

Regulation of ENaC and CFTR expression with K+channel modulators and effect on fluid absorption across alveolar epithelial cells

“…cDNAs were amplified with Taq polymerase (Invitrogen), using specific primers designed from sequences of the following cloned K ϩ channels: rat KvLQT1 (Ref. 27, GenBank Accession No. AJ133685), Slo1 (GenBank Accession No.…”

Female Gender-specific Inhibition of KCNQ1 Channels and Chloride Secretion by 17β-Estradiol in Rat Distal Colonic Crypts

“…In rat distal colon the basolateral K ϩ conductance is formed by at least two different types of K ϩ channels, activated by Ca 2ϩ or cAMP-dependent agonists (8). Electrophysiological studies in these cells have revealed the candidate K ϩ channel involved in Cl Ϫ secretion to be KCNQ1, a low conductance (1-3 pS) K ϩ channel, which is activated during cAMP-stimulated Cl Ϫ secretion (9). Other types of K ϩ channels have also been implicated in chloride secretion, including the Ca 2ϩ -dependent KCNN4 channel (10).…”

“…The rat KCNQ1 channel was cloned from colonic tissue and expression was demonstrated in both the crypt and surface cells (9). KCNQ1 is a voltage-gated channel, which plays a crucial role in controlling salt and water homeostasis in a number of epithelia (11).…”

Estrogen inhibits chloride secretion caused by cholera and Escherichia coli enterotoxins in female rat distal colon

“…In order to maintain the membrane potential at rest and during Cl -secretion, K + must be recycled out of the cell across the basolateral membrane [3]. In rat distal colonic epithelia, which is a widely used animal model for the study of intestinal Cl -secretion, the basolateral K + conductance is formed by at least two different types of K + channels, one activated by Ca 2+ -mobilizing secretagogues and the other by cAMP-dependent agonists [4,5]. Several studies have revealed the latter to be KCNQ1, a low-conductance (1-3 pS) basolateral K + channel which is activated during cAMP-stimulated Cl -secretion and inhibited by chromanol 293B and HMR-1556 [6,7].…”