Comparison of apical and basal surfaces of confluent endothelial cells: patch-clamp and viral studies

The distribution of inwardly rectifying (Ki) and calcium-activated (KCa) potassium channels on the apical and basal surfaces of bovine aortic endothelial cells (BAECs) was examined by inverting BAEC monolayers onto polylysine-coated cover slips. To monitor cellular polarity, we examined human red blood cell adherence (hemadsorption) to the influenza virus protein, hemagglutinin (HA), and virus budding on the surface of infected BAECs. Hemadsorption and virus budding occurred on the apical surface but were not apparent on the basal surface of monolayers 1 and 5 h after inversion, although cellular HA antigen localization confirmed that all monolayers were infected. In contrast, by 9.5 and 24 h after inversion, hemadsorption was evident on the "new" apical surface. Single-channel patch-clamp analysis revealed the presence of both Ki and KCa channels on the apical surface and basal surface of BAEC monolayers 2-5 h after inversion. K channel conductance and kinetics were similar regardless of the surface monitored. This nonenzymatic mechanical technique of exposing the basal surface of endothelium provides a useful tool to study the distribution of ion channels in endothelium and in other polarized cell types grown in tissue culture.