Abstract
Gap‐junction plaques are often observed with tight‐junction strands of vascular endothelial cells but the molecular interaction and functional relationships between these two junctions remain obscure. We herein show that gap‐junction proteins connexin40 (Cx40) and Cx43 are colocalized and coprecipitated with tight‐junction molecules occludin, claudin‐5, and ZO‐1 in porcine blood–brain barrier (BBB) endothelial cells. Gap junction blockers 18β‐glycyrrhetinic acid (18β‐GA) and oleamide (OA) did not influence expression of Cx40, Cx43, occludin, claudin‐5, junctional adhesion molecule (JAM)‐A, JAM‐B, JAM‐C, or ZO‐1, or their subcellular localization in the porcine BBB endothelial cells. In contrast, these gap‐junction blocking agents inhibited the barrier function of tight junctions in cells, determined by measurement of transendothelial electrical resistance and paracellular flux of mannitol and inulin. 18β‐GA also significantly reduced the barrier property in rat lung endothelial (RLE) cells expressing doxycycline‐induced claudin‐1, but did not change the interaction between Cx43 and either claudin‐1 or ZO‐1, nor their expression levels or subcellular distribution. These findings suggest that Cx40‐ and/or Cx43‐based gap junctions might be required to maintain the endothelial barrier function without altering the expression and localization of the tight‐junction components analyzed. © 2006 Wiley‐Liss, Inc.