RECEPTORS COUPLED TO PERTUSSIS-TOXIN-SENSITIVE G-PROTEINS TRAFFIC TO OPPOSITE SURFACES IN MADIN-DARBY CANINE KIDNEY-CELLS - A(1) ADENOSINE RECEPTORS ACHIEVE APICAL AND ALPHA(2A) ADRENERGIC-RECEPTORS ACHIEVE BASOLATERAL LOCALIZATION

The alpha(2A) adrenergic receptor (alpha(2A)AR) previously was shown t o be directly delivered to and retained on the lateral subdomain of re nal epithelial cells. The present studies demonstrate that, in contras t, wild-type and epitope-tagged canine A(1) adenosine receptors (A(1)A doR) are apically enriched (65-83%) in Madin-Darby canine kidney (MDCK II) and porcine renal epithelial (LLC-PKI) cells, based on surface bio tinylation strategies detecting photoaffinity-labeled A(1)AdoR. Confoc al micros copy corroborated the apical enrichment of the epitope-tagge d A(1)AdoR. Metabolic labeling studies revealed that this steady-state polarization is achieved by direct delivery to both the apical (60-75 %) and basolateral surface. Growth of A(1)AdoR-expressing cells as mon olayers was achieved only following Transwell culture in the presence of A(1)AdoR antagonists, which decreased cell growth, suggesting that A(1)AdoR elicit MDCKII cell proliferation. The preferential apical but detectable basolateral localization of A(1)AdoR provides a molecular understanding of published reports that functional responses can be el icited following apical as well as basolateral delivery of adenosine a gonists in varying renal preparations. These findings also suggest tha t receptor chimeras derived from the G(i)/G(o)-protein-coupled alpha(2 A)AR and A(1)AdoR will be informative in revealing structural features critical for basolateral versus apical targeting.