title: Basolateral K+ channel involvement in forskolin-activated chloride secretion in human colon.
abstract: 1. In this study we investigated the role of basolateral potassium transport in maintaining cAMP-activated chloride secretion in human colonic epithelium. 2. Ion transport was quantified in isolated human colonic epithelium using the short-circuit current technique. Basolateral potassium transport was studied using nystatin permeabilization. Intracellular calcium measurements were obtained from isolated human colonic crypts using fura-2 spectrofluorescence imaging. 3. In intact isolated colonic strips, forskolin and prostaglandin E2 (PGE2) activated an inward transmembrane current (ISC) consistent with anion secretion (for forskolin DeltaISC = 63.8+/-6.2 microA cm(-2), n = 6; for PGE2 DeltaISC = 34.3+/-5.2 microA cm(-2), n = 6). This current was inhibited in chloride-free Krebs solution or by inhibiting basolateral chloride uptake with bumetanide and 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid DIDS). 4. The forskolin- and PGE2-induced chloride secretion was inhibited by basolateral exposure to barium (5 mM), tetrapentylammonium (10 microM) and tetraethylammonium (10 mM). 5. The transepithelial current produced under an apical to serosal K+ gradient in nystatin-perforated colon is generated at the basolateral membrane by K+ transport. Forskolin failed to activate this current under conditions of high or low calcium and failed to increase the levels of intracellular calcium in isolated crypts 6. In conclusion, we propose that potassium recycling through basolateral K+ channels is essential for cAMP-activated chloride secretion.
authors.affiliation: Wellcome Trust Cellular Physiology Research Unit, Department of Physiology, University College Cork, Mercy Hospital, Cork, Ireland. b.mcnamara@medschl.cam.ac.uk
authors.forename: B
authors.initials: B
authors.lastname: McNamara
authors.forename: D C
authors.initials: DC
authors.lastname: Winter
authors.forename: J E
authors.initials: JE
authors.lastname: Cuffe
authors.forename: G C
authors.initials: GC
authors.lastname: O'Sullivan
authors.forename: B J
authors.initials: BJ
authors.lastname: Harvey
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002034:Bumetanide / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D002712:Chlorides / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology*; D003106:Colon / Q000502:physiology*; D006801:Humans; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008954:Models, Biological; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000502:physiology*; D012964:Sodium / Q000378:metabolism; D019789:Tetraethylammonium / Q000494:pharmacology; D014044:Tolbutamide / Q000494:pharmacology
chemical_list: D002712:Chlorides; D015221:Potassium Channels; D002034:Bumetanide; D005576:Colforsin; D019789:Tetraethylammonium; D014044:Tolbutamide; D012964:Sodium; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D011188:Potassium; D002118:Calcium