title: Permeation, selectivity, and blockade of the Ca2+-activated potassium channel of the guinea pig taenia coli myocyte.
abstract: The permeation properties of the 147-pS Ca2+-activated K+ channel of the taenia coli myocytes are similar to those of the delayed rectifier channel in other excitable membranes. It has a selectivity sequence of K+ 1.0 greater than Rb+ 0.65 greater than NH4+ 0.50. Na+, Cs+, Li+, and TEA+ (tetraethylammonium) are impermeant. Internal Na+ blocks K+ channel in a strongly voltage-dependent manner with an equivalent valence (zd) of 1.20. Blockade by internal Cs+ and TEA+ is less voltage dependent, with d of 0.61 and 0.13, and half-blockage concentrations of 88 and 31 mM, respectively. External TEA+ is about 100 times more effective in blocking the K+ channel. All these findings suggest that the 147-pS Ca2+-activated K+ channel in the taenia myocytes, which functions physiologically like the delayed rectifier, is the single-channel basis of the repolarizing current in an action potential.
authors.affiliation: Department of Pharmacology, State University of New York, Brooklyn 11203.
authors.forename: S L
authors.initials: SL
authors.lastname: Hu
authors.forename: Y
authors.initials: Y
authors.lastname: Yamamoto
authors.forename: C Y
authors.initials: CY
authors.lastname: Kao
mesh_terms: D000641:Ammonia / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002414:Cations, Monovalent; D002463:Cell Membrane Permeability; D002586:Cesium / Q000378:metabolism / Q000494:pharmacology; D003106:Colon / Q000378:metabolism; D006168:Guinea Pigs; D008094:Lithium / Q000378:metabolism; D008564:Membrane Potentials; D009130:Muscle, Smooth / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D012413:Rubidium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000378:metabolism / Q000494:pharmacology
chemical_list: D002414:Cations, Monovalent; D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D002586:Cesium; D019789:Tetraethylammonium; D000641:Ammonia; D008094:Lithium; D012964:Sodium; D012413:Rubidium; D011188:Potassium; D002118:Calcium