Cholesterol-dependent regulation of adenosine A(2A) receptor-mediated anion secretion in colon epithelial cells.

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.