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Pericyte‐endothelial junctional communication and calcium coupling (664.8)

Pericytes (PCs) initiate and maintain the blood‐brain barrier phenotype of cerebral endothelium. Despite many studies referencing pericyte‐endothelial junctional (PEJ) communication, little is known of this signaling pathway. The purpose of this study was to determine if human brain endothelial cells (ECs) and PCs are functionally coupled. ECs and PCs were loaded with the calcium indicator fluo‐4 AM (Invitrogen) and treated with different reagents of varying concentrations (10‐4 to 10‐8 M). ECs and PCs both responded to acetylcholine, caffeine, and bradykinin (BK). Neither cell type responded to phenylephrine. Only PCs were stimulated by low concentrations (10‐7 M) of angiotensin 2. The magnitudes of responses to BK were higher in PCs than ECs at all concentrations tested (p< 0.05). To determine whether the PEJ mediates calcium coupling between cells, respective cell types were cultured on opposite sides of membrane inserts and loaded with fluo‐4 AM (0.4 µm pores; Transwell, Corning). BK concentrations ranging from 10‐5 to 10‐7 M elicited robust EC responses when applied to the PC side but were absent when PCs were removed. Immuno‐positive labeling of connexin 45 (Cx45), but not connexins 37, 40, or 43, in membrane pores is consistent with the presence of Cx45‐based gap junctional coupling at the PEJ. Human brain ECs and PCs form functional cell‐cell junctions, PEJs, which facilitate intercellular calcium signaling. This pathway may play a role in the regulation of blood‐brain barrier properties, possibly through Cx45‐dependent signaling.