title: Cholesterol-dependent regulation of adenosine A(2A) receptor-mediated anion secretion in colon epithelial cells.
abstract: Cholesterol affects diverse biological processes, in many cases by modulating the function of integral membrane proteins. In this study we have investigated the role of cholesterol in the adenosine-dependent regulation of ion transport in colonic epithelial cells. We observed that methyl-beta-cyclodextrin (MbetaCD), a cholesterol-sequestering molecule, enhanced adenosine A(2A) receptor-activated transepithelial short circuit current (I(sc)), but only from the basolateral side. Cholesterol is a major constituent of membrane microdomains, called lipid rafts that also contain sphingolipids. However, studies with the sphingomyelin-degrading enzyme, sphingomyelinase, and the cholesterol-binding agent, filipin, indicated that the change in the level of cholesterol alone was sufficient to control the adenosine-modulated I(sc). Cholesterol depletion had a major effect on the functional selectivity of A(2A) receptors. Under control conditions, adenosine activated I(sc) more potently than the specific A(2A) agonist, CGS-21680, and the current was inhibited by XE991, an inhibitor of cAMP-dependent K(+) channels. Following cholesterol depletion, CGS-21680 activated I(sc) more potently than adenosine, and the current was inhibited by clotrimazole, an inhibitor of Ca(2+)-activated K(+) (IK1) channels. Co-immunoprecipitation experiments revealed that A(2A) receptors associate with IK1 channels following cholesterol depletion. These results suggest that cholesterol content in colonic epithelia affects adenosine-mediated anion secretion by controlling agonist-selective signaling.
authors.affiliation: Department of Physiology, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Rebecca S
authors.initials: RS
authors.lastname: Lam
authors.forename: Drew
authors.initials: D
authors.lastname: Nahirney
authors.forename: Marek
authors.initials: M
authors.lastname: Duszyk
mesh_terms: D019830:Adenosine-5'-(N-ethylcarboxamide) / Q000494:pharmacology; D000818:Animals; D051242:Caveolin 1 / Q000172:deficiency / Q000235:genetics; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D002784:Cholesterol / Q000494:pharmacology*; D003106:Colon / Q000378:metabolism / Q000502:physiology*; D006706:Homeostasis / Q000187:drug effects / Q000502:physiology; D007413:Intestinal Mucosa / Q000378:metabolism / Q000502:physiology*; D007700:Kinetics; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D043705:Receptor, Adenosine A2A / Q000187:drug effects / Q000502:physiology*
chemical_list: D051242:Caveolin 1; D043705:Receptor, Adenosine A2A; D019830:Adenosine-5'-(N-ethylcarboxamide); D002784:Cholesterol