Histamine-induced Changes in the Actin Cytoskeleton of the Human Microvascular Endothelial Cell line HMEC-1

Increased permeability of the microvascular endothelium is a component of the inflammatory response. Inflammatory mediators such as histamine contribute to this permeability change. Modulation of cytoskeletal F-actin has been implicated as part of the cellular mechanism involved. Permeability changes occur predominantly at the microvascular level while the majority of current knowledge stems from research on cells from large vessels. We have therefore utilized an immortalized human dermal microvascular cell line, HMEC-1. Confluent monolayers were exposed to histamine (10 mum, 100 mum) for 1, 5, 10 or 15 minutes. F-Actin changes were detected by labelling with FITC-conjugated phalloidin. Histamine exposure resulted in the rounding of cells with the formation of intercellular gaps. The percentage of rounded cells and the number of gaps increased with exposure time. F-actin was redistributed from a peripheral band in control cultures to a perinuclear zone. Continual presence of the agonist was required for these phenotypic changes to occur. Removal of histamine caused reversal of these observations. Cells exposed to histamine for 1 minute needed 15 minutes to recover their normal morphology and F-actin distribution. These reversible effects suggest that F-actin redistribution maybe part of the microvascular cell response to histamine.