Basolateral but not apical VEGF stimulation induces microvascular permeability

Vascular endothelial growth factor (VEGF) potently induces permeability in vitro and vivo. Here, we show that vasoactive effects of VEGF are restricted to stimulation on the abluminal side of microvascular endothelial cells (MVECs). Apical stimulation of primary rat cerebral or retinal MVECs with thrombin or LPA but not VEGF or histamine, reduced impedance, enhanced macromolecular flux and caused a transient loss of the tight junction protein claudin-5. In contrast, VEGF had to be applied basolaterally to induce a similar vasoactive response. This sided response was only observed in EC monolayers of high electrical resistance (> 200 Ωcm2) and was lost when cells were passaged, suggesting that cell polarity was essential. A similar sidedness in the response to VEGF was observed in vivo. The permeability to sulforhodamine of single venular capillaries of rats (anaesthetized with hypnorm/hypnoval: 10 mg.kg-1 i.p., in accordance with current UK legislation) was measured. Topically applied VEGF induced a strong surge in pial venular permeability whereas luminal delivery was without any effect. Significantly, both apical and basolateral VEGF induced signalling in MVECs, but the activated signalling pathways and the time course of their activation were clearly distinct. We conclude that VEGF signalling is highly polarised in brain and retinal microvessels and that will define the effectiveness of anti-VEGF therapies.