Mitochondrial dysfunction is intimately involved in cardiovascular diseases. Mitochondrial membrane potential (Delta Psi(m)) is coupled with oxidative phosphorylation to drive ATP synthesis. In this study, we examined the effect of physiological pulsatile shear stress (PSS) on Delta Psi(m) and the role of Mn-SOD expression on Delta Psi(m). Confluent human aortic endothelial cells (HAEC) were exposed to PSS, and Delta Psi(m) was monitored using tetramethylrhodamine methyl ester (TMRM+), a mitochondrial membrane potential probe. PSS significantly increased Delta Psi(m) and the change in Delta Psi(m) was a dynamic process. Delta Psi(m) returned to baseline level after PSS for 2 h followed by static state for 4 h. Mitochondrial Mn-SOD expression and activities were also significantly up-regulated in response to PSS. Silencing Mn-SOD attenuated PSS-mediated Delta Psi(m) increase while adding Mn-SOD mimetic, MnTMPyP, increased Delta Psi(m) to the similar extent as induced by PSS. Our findings suggest that PSS-increased mitochondrial Delta Psi(m), in part, via Mn-SOD up-regulation. (C) 2009 Elsevier Inc. All rights reserved.