Objective—The aim of this study was to examine the endothelial distribution and activity of selected PKC isoforms in coronary vessels with respect to their functional impact on endothelial permeability under the experimental conditions relevant to diabetes.

Methods and Results—En face immunohistochemistry demonstrated a significant increase of PKC_II and decrease of PKC expression in coronary arterial endothelium of Zucker diabetic rats. To test whether changes in PKC expression alter endothelial barrier properties, we measured the transcellular electric resistance in human coronary microvascular endothelial monolayers and found that either PKC_II overexpression or PKC inhibition disrupted the cell–cell adhesive barrier. Three-dimensional fluorescence microscopy revealed that hyperpermeability was caused by altered PKC activity in association with distinct translocation of PKC_II to the cell–cell junction and PKC localization to the cytosol. Further analyses in fractionated endothelial lysates confirmed the differential redistribution of these isozymes. Additionally, FRET analysis of PKC subcellular dynamics demonstrated a high PKC_II activity at the cell surface and junction, whereas PKC activity is concentrated in intracellular membrane organelles.

Conclusion—Taken together, these data suggest that PKC_II and PKC counter-regulate coronary endothelial barrier properties by targeting distinctive subcellular sites. Imbalanced PKC_II/PKC expression and activity may contribute to endothelial hyperpermeability and coronary dysfunction in diabetes.