Abstract
During angiogenesis in the chick chorioallantoic membrane (CAM), microvascular proliferation continues through day 12 of the 18-day CAM lifespan. Up to day 4.5, the neovascularization is associated with endothelial hyperpermeability and differentiation of restrictive barrier function occurs abruptly at day 5.0. Although exogenous activation of cAMP/protein kinase A (PKA) signaling served to decrease macromolecular extravasation at day 4.5, endogenous signaling cascades responsible for the temporal hyperpermeability remain uncertain. Here, we evaluated protein kinase C (PKC) function in the CAM endothelium at day 4.5 and day 5.0. The specific, broad-based PKC inhibitor calphostin C reduced basal levels of FITC-dextran 40 extravasation at day 4.5. Bisindolymaleimide (BIM), which inhibits selective PKC isoforms, also reduced temporal FITC-dextran 40 efflux, but to a lesser extent than calphostin C. Activation of PKC activity by phorbol-12, 13-didecanoate (PDD) or phorbol-12, 13-dibutyrate (PDBu) at day 5.0 served to partially de-differentiate barrier properties of the angiogenic endothelium. The associated elevation of FITC-dextran 40 extravasation occurred without interendothelial gap formation along the junctional clefts. Together, these results are consistent with the interpretation that PKC activity contributes, in part, to CAM endothelial hyperpermeability at day 4.5. Furthermore, down-regulation of PKC signaling correlates temporally with the ontogeny of restrictive barrier function at day 5.0.