Expression of intermediate conductance potassium channel immunoreactivity in neurons and epithelial cells of the rat gastrointestinal tract

Abstract

Recent functional evidence suggests that intermediate conductance calcium-activated potassium channels (IK channels) occur in neurons in the small intestine and in mucosal epithelial cells in the colon. This study was undertaken to investigate whether IK channel immunoreactivity occurs at these and at other sites in the gastrointestinal tract of the rat. IK channel immunoreactivity was found in nerve cell bodies throughout the gastrointestinal tract, from the esophagus to the rectum. It was revealed in the initial segments of the axons, but not in axon terminals. The majority of immunoreactive neurons had Dogiel type II morphology and in the myenteric plexus of the ileum all immunoreactive neurons were of this shape. Intrinsic primary afferent neurons in the rat small intestine are Dogiel type II neurons that are immunoreactive for calretinin, and it was found that almost all the IK channel immunoreactive neurons were also calretinin immunoreactive. IK channel immunoreactivity also occurred in calretinin-immunoreactive, Dogiel type II neurons in the caecum. Epithelial cells of the mucosal lining were immunoreactive in the esophagus, stomach, small and large intestines. In the intestines, the immunoreactivity occurred in transporting enterocytes, but not in mucous cells. Immunoreactivity was at both the apical and basolateral surfaces. A small proportion of mucosal endocrine cells was immunoreactive in the duodenum, ileum and caecum, but not in the stomach, proximal colon, distal colon or rectum. There was immunoreactivity of vascular endothelial cells. It is concluded that IK channels are located on cell bodies and proximal parts of axons of intrinsic primary afferent neurons, where, from functional studies, they would be predicted to lower neuronal excitability when opened in response to calcium entry. In the mucosa of the small and large intestine, IK channels are probably involved in control of potassium exchange, and in the esophageal and gastric mucosa they are possibly involved in control of cell volume in response to osmotic challenge.

A Functional Role for Small-Conductance Calcium-Activated Potassium Channels in Sensory Pathways Including Nociceptive Processes

“…3 A, B). As with the staining for SK3, the ependymal cells, by expressing IK1, are like other types of epithelial cells, which have been reported to express similarly high levels of the SK and IK channels (MacVinish et al, 1998;Furness et al, 2003;Rhodes et al, 2003). In addition, IK immunoreactivity also appears in the bodies of cells scattered throughout the spinal cord (Fig.…”

Characteristics of Kcnn4 channels in the apical membranes of an intestinal epithelial cell line

“…basolateral membrane; intermediate-conductance potassium channel isoforms; potassium secretion; patch clamp INTERMEDIATE-CONDUCTANCE K ϩ (Kcnn4) channels (also known as IK1, mIK1, and K Ca 3.1) are Ca 2ϩ -dependent K ϩ channels of intermediate conductance that are broadly distributed in both nonepithelial and epithelial cells where they play important roles in regulating membrane potential, influencing Ca 2ϩ signaling, maintaining cell volume, and providing the driving force for anion (Cl Ϫ and HCO 3 Ϫ ) secretion (12,18,24,26). Kcnn4 channels are present on both apical and basolateral membranes of epithelial cells, including human bronchial (16HBE140 cell line), pancreatic duct adenocarcinoma (HPAF cell line), small intestine, and colon (1,3,6,9,25). In a recent study, we isolated from rat colon three distinct Kcnn4 splice variants: Kcnn4a, Kcnn4b, and Kcnn4c, which encoded proteins of 425, 424, and 395 amino acids, respectively (1).…”

“…The monolayer exhibits a net electrical resistance that is similar to the intact epithelial layer of rat small intestine (15), and it lacks the layer of mucus that interferes with patch seal formation. Our choice of this cell line was also justified by immunofluoresence studies that have localized Kcnn4-like proteins on both the apical and basolateral membranes of surface and crypt cells in rat ileum (6). We report here that we successfully characterized the physiological properties of Kcnn4 channels in the apical membrane of IEC-18 cells.…”

“…Immunofluoresence and functional studies have shown that Kcnn4 channels are localized on both the apical and basolateral membranes of intestinal and colonic epithelial cells in human, guinea pig, and rat (6,9,12,21). Molecular studies have identified the Kcnn4 channel as the basolateral K ϩ channel that provides the driving force for anion secretion (12,26).…”

Cyclic AMP-induced K+secretion occurs independently of Cl−secretion in rat distal colon

“…Intermediate-conductance, Ca 2ϩ -activated K ϩ channels localized to the basolateral membrane have been shown to provide the driving force for agonist (Ca 2ϩ , cAMP)-induced Cl Ϫ secretion in human and mouse colon (22,23 -activated K ϩ channel 3.1, and Kcnn4 (14,17,30). Immunofluorescence studies have localized Kcnn4-like proteins to both the apical and basolateral membranes of human, guinea pig, and rat colon (3,10,11). The splice variants Kcnn4c and Kcnn4b have been shown to encode apical and basolateral Kcnn4 channels in rat distal colon (3).…”