Connexin channels provide a target to manipulate brain endothelial calcium dynamics and blood brain barrier permeability

Aims: The cytoplasmic calcium concentration ([Ca2+]i) is an important factor determining the permeability of endothelial cell layers but little is known on the effect of [Ca2+]i dynamics on endothelial function. Here, we applied several conditions that trigger [Ca2+]i oscillations and cell-to-cell propagating Ca2+ waves, and determined the involvement of connexin channels and consequent effects on endothelial barrier function, in model systems based on immortalized and primary brain endothelial cells. Methods and Results: Exposure to low extracellular Ca2+ or bradykinin respectively triggered Ca2+ waves or oscillations that increased endothelial permeability in a [Ca2+]i-dependent manner. Both Ca2+ waves/oscillations and permeability alterations were inhibited by the connexin mimetic peptide Gap27. Ca2+ wave propagation involves gap junctional communication and opening of hemichannels but open hemichannels did not contribute as a permeability-increasing pathway. Ca2+ oscillations were inhibited by Cx37/43 knockdown and involved hemichannel opening as well as autocrine purinergic signaling. However, hemichannels were, as for Ca2+ waves, not the pathway of increased endothelial permeability. Exposure to ATP triggered, like bradykinin, Ca2+ oscillations but in contrast, those were not affected by Gap27 and did not disturb permeability. Conclusion: We conclude that connexin channels and purinergic signaling actively contribute to endothelial [Ca2+]i dynamics and are important to modulate endothelial permeability.