MLC1 and endothelial dysfunction: Conversely, phosphorylation of myosin regulatory light chain (MLC) not only increases actomyosin ATPase activity, but also destabilizes the endothelial cell−cell junctions leading to increased monolayer cell permeability [26], [16], [27].Our results are encouraging and they warrant future research on demonstrating whether ectopic expression of Myl9 in the aged endothelium causes endothelial dysfunction.