Receptors coupled to pertussis toxin-sensitive G-proteins traffic to opposite surfaces in Madin-Darby canine kidney cells A₁ adenosine receptors achieve apical and α_2A adrenergic receptors achieve basolateral localization

The α_2A adrenergic receptor (α_2AAR) previously was shown to be directly delivered to and retained on the lateral subdomain of renal epithelial cells. The present studies demonstrate that, in contrast, wild-type and epitope-tagged canine A₁ adenosine receptors (A₁AdoR) are apically enriched (65-83%) in Madin-Darby canine kidney (MDCKII) and porcine renal epithelial (LLC-PKI) cells, based on surface biotinylation strategies detecting photoaffinity-labeled A₁AdoR. Confocal microscopy corroborated the apical enrichment of the epitopetagged A₁AdoR. 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 A₁AdoR-expressing cells as monolayers was achieved only following Transwell culture in the presence of A₁AdoR antagonists, which decreased cell growth, suggesting that A₁AdoR elicit MDCKII cell proliferation. The preferential apical but detectable basolateral localization of A₁AdoR provides a molecular understanding of published reports that functional responses can be elicited following apical as well as basolateral delivery of adenosine agonists in varying renal preparations. These findings also suggest that receptor chimeras derived from the G_i/G_o-protein-coupled α_2AAR and A₁AdoR will be informative in revealing structural features critical for basolateral versus apical targeting.