TY - JOUR T1 - Microtubule-Dependent Regulation of α<sub>2B</sub> Adrenergic Receptors in Polarized MDCKII Cells Requires the Third Intracellular Loop but Not G Protein Coupling JF - Molecular Pharmacology JO - Mol Pharmacol SP - 44 LP - 52 VL - 57 IS - 1 AU - Christine Saunders AU - Lee E. Limbird Y1 - 2000/01/01 UR - http://molpharm.aspetjournals.org/content/57/1/44.abstract N2 - Previous studies in cultured, polarized Madin-Darby canine kidney II (MDCKII) renal epithelial cells have demonstrated that the apical steady-state localization and delivery of the A1 adenosine receptor is modified by disruption of the microtubule network with colchicine, whereas the basolateral localization and trafficking of the α2-adrenergic receptors (α2AR) are not; instead, the binding capacity of the α2BAR, but not α2AAR or α2CAR subtypes, is increased in a time-dependent fashion. The present studies explore the molecular basis for this α2BAR subtype-selective phenomenon. Colchicine selectively increased α2BAR density at the cell surface, as determined by confocal microscopy, receptor binding, and surface biotinylation studies. The colchicine-induced increase in the functional density of the α2BAR requires the third intracellular loop because the α2BAR loop deletion (α2BAR▵i3) mutant did not show an increased receptor density after colchicine treatment. Furthermore, the colchicine-mediated increase in α2BAR density is manifest only in polarized cells because colchicine treatment of nonpolarized MDCKII renal epithelial cells as well as simian kidney COSM6 and human embryonic kidney HEK293 cells did not effect an increase in α2BAR density. Colchicine-dependent increases in α2BAR density did not depend on functional coupling to G proteins, however, because pretreatment with pertussis toxin did not eliminate the effect of colchicine. These data indicate that microtubule-dependent regulation of α2BAR density at the basolateral surface of polarized MDCKII cells requires the third intracellular loop of α2BAR but not functional α2BAR-G protein coupling. The American Society for Pharmacology and Experimental Therapeutics ER -