Histamine selectively interrupts VE-cadherin adhesion independently of capacitive calcium entry

Histamine is an important agent of innate immunity, transiently increasing the flux of immune-competent molecules from the vascular space to the tissues and then allowing rapid restoration of the integrity of the endothelial barrier. In previous work we found that histamine alters the endothelial barrier by disrupting cell-cell adhesion and identified VE-cadherin as an essential participant in this process. The previous work did not determine whether histamine directly interrupted VE-cadherin adhesion, whether the effects of histamine were selective for cadherin adhesion, or whether capacitive calcium flux across the cell membrane was necessary for the effects of histamine on cell-cell adhesion. In the current work we found that histamine directly interrupts adhesion of L cells expressing the type 1 histamine (H1) receptor and VE-cadherin to a VE-cadherin-Fc fusion protein. In contrast, integrin-mediated adhesion to fibronectin of the same L cells expressing the H1 receptor was not affected by histamine, demonstrating that the effects of histamine are selective for cadherin adhesion. Some of the effects of many edemagenic agonists on endothelium are dependent on the capacitive flux of calcium across the endothelial cell membrane. Blocking capacitive calcium flux with LaCl3 did not prevent histamine from interrupting VE-cadherin adhesion of transfected L cells, nor did it prevent histamine from interrupting cell-cell adhesion of human umbilical vein endothelial cells. These data support the contentions that histamine directly and selectively interrupts cadherin adhesion and this effect on cadherin adhesion is independent of capacitive calcium flux. endothelium; integrin; human histamine receptor H1; vascular endothelial cadherin ACUTE INFLAMMATORY EDEMA is an important component of innate immunity that facilitates the transfer of immune-competent molecules from the vascular space to the tissues. Histamine and serotonin are well-acknowledged physiological agonists of acute inflammatory edema that disrupt cell-cell apposition in postcapillary venules Vascular endothelial (VE)-cadherin is an endothelial unique cadherin that mediates cell-cell adhesion of endothelial cells (17). Function-interrupting antibody to VE-cadherin increases permeability of endothelium in vivo, indicating that integrity of VE-cadherin adhesion is essential to the integrity of the endothelial barrier (9, 16). It was of note that although antibody to VE-cadherin increased in vivo endothelial permeability within 1 h of its administration, no light microscopic changes were evident in the endothelium even at 2 h, demonstrating that no large gaps had formed between the cells. However, similar to the effects of histamine and serotonin, transmission electron micrographs detected very small gaps in lung microvessels exposed to antibody to VE-cadherin (9). ECV304 cells are a transformed bladder epithelial cell line that express the type 1 histamine receptor (H1) and P-and N-cadherin, but not VE-cadherin. When mock-transfected ECV304 cells were exposed to histamine, there was no change in the electrical resistance of the cell-cell barrier they created (24). However, when ECV304 cells transfected with VEcadherin were exposed to histamine, the electrical resistance of the cell-cell barrier fell, identifying an important role for VE-cadherin in the response to histamine of a monolayer of polarized cells (24). ECV304 cells express claudin 2 and develop tight junctions (5). This tight junction is a necessary component of the electrical resistance decreased by histamine. The observation that histamine decreased the integrity of the cell-cell barrier created by VE-cadherin transfected ECV304 cells did not discriminate between effects of histamine on an interaction of VE-cadherin with the tight junction versus a direct effect of histamine on VE-cadherin adhesion. Histamine and other agonists that increase endothelial permeability initiate signaling in endothelial cells that increases cell calcium (6, 7). Although some of the increase in cell calcium caused by these agonists reflects release of calcium from intracellular stores, capacitive flux of calcium across the cell membrane is also activated, and the capacitive calcium flux is necessary for some of the effects of these agonists on endothelial cells In these investigations we used a model of cadherin adhesion that lacks tight junctions and asked whether histamine directly affects VE-cadherin adhesion as opposed to affecting an interaction between VE-cadherin and the tight junction. Our results indicate that histamine directly affects VE-cadherin adhesion. Using a similar model of integrin-based adhesion, we foun