Molecular and functional characterization of the small Ca 2+ -regulated K + channel (rSK4) of colonic crypts

Abstract

Colonic crypt cells possess basolateral Ca(2+)-regulated K+ channels which support Cl- secretion by providing the necessary driving force. The pharmacological characteristics of these channels were examined in Ussing chamber experiments of rat and rabbit colon mucosa by the use of blockers. The chromanol 293B, a blocker of KVLQT1 channels, and clotrimazole (CTZ), a blocker of small Ca(2+)-activated K+ channels, blocked stimulated Cl- secretion completely. Small-conductance Ca(2+)-activated K+ channels (SK) in excised basolateral patches of rat colonic crypts were inhibited concentration dependently by the imidazoles CTZ, NS004 and NS1619 and activated by 1-EBIO. These properties are similar to those of the known human SK channel (hSK4). hSK4-expressing Xenopus laevis oocytes showed ionomycin-activated and CTZ-inhibited K+ currents. When P2Y2 receptors were coexpressed these currents were also activated by ATP. The concentration/response curve was identical to that of rat SK channels. In human colonocytes (T84) exposed to hSK4 antisense probes, but not to sense probes, carbachol-induced K+ currents were attenuated. With RT-PCR an hSK4 could be demonstrated in human colon and in T84 colonocytes. By homology cloning the SK of the rat colon (rSK4) was identified. This protein has a high homology to hSK4 and mouse IK1. These data indicate that the Ca(2+)-activated and imidazole-inhibited basolateral K+ current in the colon is caused by SK4 channels.

SK4/IK1-like channels mediate TEA-insensitive, Ca2+-activated K+ currents in bovine parotid acinar cells

“…Ca 2ϩ (1 M)-activated hSK4/IK1-like K ϩ currents in T84 cells, in which transcripts of hSK4/IK1 are expressed, have been shown to be blocked by intracellular Ba 2ϩ but not by extracellular Ba 2ϩ (9,23). We also extended the pharmacological study to include 1-EBIO, which has been shown to increase both the heterologously expressed SK4/IK1 (30,32,35,43,51,52) and other native SK4/IK1-like currents (10,32,52). As expected from the striking resemblance between native bovine K Ca and expressed SK4/IK1 currents, the native Ca 2ϩ -activated Rb ϩ currents were modulated by 1-EBIO (Fig.…”

“…Recent molecular studies have identified four members (SK1-3 and SK4/IK1) of K Ca channels that form Ca 2ϩ -activated, small-to intermediate-conductance K ϩ channels in various excitable and nonexcitable tissues. SK1-3 channels are predominantly expressed in excitable tissues (50), whereas SK4/IK1 channels are expressed in peripheral nonexcitable cells including secretory epithelia (24,30,31,52), erythrocytes (49), and lymphocytes (32,35). Intriguingly, Jensen et al (30) reported that the highest level of transcripts of hSK4/IK1 was expressed in salivary glands.…”

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].…”

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

“…Both types take part in Cl -secretion in rat colon: Ca 2+ -dependent rSK4 channels (Warth et al, 1999) and cyclic AMP-activated KCNQ1/KCNE3 channels (Schroeder et al, 2000). Activated channels hyperpolarize (EGTA) free buffer.…”