Under conditions where apoptosis is prevented, peroxides disrupt the endothelial monolayer by inducing cytoskeletal rearrangements, cell retraction and formation of arrays of membrane blebs. In human umbilical vein endothelial cells (HUVEC), the H(2)O(2)-induced membrane blebbing was found to be a transient process executed by two parallel signaling mechanisms: (i) mobilization of cytosolic [Ca(2+)](i) through a pathway requiring oxidation of reduced glutathione (GSH), and (ii) activation of p38 mitogen-activated protein kinases (MAPK) independently of GSH oxidation and Ca(2+) mobilization. In the HUVEC, membrane blebbing was thus blocked by inhibition of GSH oxidation, Ca(2+) mobilization or p38 MAPK activation. Stimulation of GSH peroxidation with ebselen potentiated the H(2)O(2)-induced oscillating Ca(2+) response and the bleb formation, but not p38 phosphorylation. Chelation of [Ca(2+)](i) abolished the blebbing process but not p38 activation. In addition, in the GSH peroxidase-resistant cell line ECV304, H(2)O(2) was unable to promote membrane blebbing or significant Ca(2+) release, while p38 became phosphorylated. However, [Ca(2+)](i) was increased and blebs were formed, when the ECV304 were treated with ebselen before H(2)O(2). Together, this leads to a model where oxidative stress, through both Ca(2+)-dependent and p38 kinase-mediated phosphorylation events, causes reassembly of the actin cytoskeleton and subsequent appearance of membrane blebs at the plasma membrane.