title: Regulation of Ca2+-activated K+ channel from rabbit distal colon epithelium by phosphorylation and dephosphorylation.
abstract: The Ca2+-activated maxi K+ channel is predominant in the basolateral membrane of the surface cells in the distal colon. It may play a role in the regulation of the aldosterone-stimulated Na+ reabsorption from the intestinal lumen. Previous measurements of these basolateral K+ channels in planar lipid bilayers and in plasma membrane vesicles have shown a very high sensitivity to Ca2+ with a K0.5 ranging from 20 nm to 300 nm, whereas other studies have a much lower sensitivity to Ca2+. To investigate whether this difference could be due to modulation by second messenger systems, the effect of phosphorylation and dephosphorylation was examined. After addition of phosphatase, the K+ channels lost their high sensitivity to Ca2+, yet they could still be activated by high concentrations of Ca2+ (10 micron). Furthermore, the high sensitivity to Ca2+ could be restored after phosphorylation catalyzed by a cAMP dependent protein kinase. There was no effect of addition of protein kinase C. In agreement with the involvement of enzymatic processes, lag periods of 30-120 sec for dephosphorylation and of 10-280 sec for phosphorylation were observed. The phosphorylation state of the channel did not influence the single channel conductance. The results demonstrate that the high sensitivity to Ca2+ of the maxi K+ channel from rabbit distal colon is a property of the phosphorylated form of the channel protein, and that the difference in Ca2+ sensitivity between the dephosphorylated and phosphorylated forms of the channel protein is more than one order of magnitude. The variety in Ca2+ sensitivities for maxi K+ channels from tissue to tissue and from different studies on the same tissue could be due to modification by second messenger systems.
authors.affiliation: Biomembrane Research Centre, The August Krogh Institute, Copenhagen University, 2100 Copenhagen O, Denmark.
authors.forename: D A
authors.initials: DA
authors.lastname: Klaerke
authors.forename: H
authors.initials: H
authors.lastname: Wiener
authors.forename: T
authors.initials: T
authors.lastname: Zeuthen
authors.forename: P L
authors.initials: PL
authors.lastname: Jorgensen
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D003106:Colon / Q000378:metabolism*; D004847:Epithelial Cells; D004848:Epithelium / Q000502:physiology; D066298:In Vitro Techniques; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism; D010766:Phosphorylation; D015221:Potassium Channels / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism; D011817:Rabbits; D015290:Second Messenger Systems
chemical_list: D015221:Potassium Channels; D011494:Protein Kinases; D010744:Phosphoric Monoester Hydrolases; D002118:Calcium