Introduction. We applied pressure stress to human aortic endothelial cells (HAEC) and investigated whether mechanical pressure stress and/or angiotensin II (Ang II) affected angiotensin-converting enzyme (ACE) 2. We then tested whether the administration of nifedipine had a demonstrable and possibly beneficial effect. Methods. A pulsatile atmospheric pressure with or without Ang II was loaded on HAECs. The expression of ACE2 was studied by immunoblots and reverse transcription/real-time polymerase chain reaction. Results. The pulsatile mechanical pressure increased the expression of ACE2 mRNA by approximately 80%. Supplementation of Ang II (1 mM) with pulsatile mechanical pressure decreased the expression of ACE2 mRNA by approximately 54%. Pulsatile atmospheric pressure increased ACE2 protein, but supplementation of Ang II (1 mM) also increased ACE2 protein, and the latter failed to show significant change compared to pressurized control without Ang II. Ang II administration reduced ACE2 protein in the membranous fraction under pressurized condition. Administration of nifedipine (1 mM) protected cells from this ACE2 protein reduction at the HAEC membrane. Conclusions. These results indicate that pulsatile mechanical pressure and Ang II affect ACE2 in HAECs. Our findings suggest that blood pressure reduction with a calcium channel blocker is beneficial for the conservation of ACE2, and may provide a potential therapeutic target beyond blood pressure lowering in hypertensive patients. IntroductionRegulation of the renin-angiotensin system is a well-established strategy that has been used for the treatment of cardiovascular diseases during the past few decades. Two types of angiotensinconverting enzyme (ACE) have been noted, and the clinical importance of conventional ACE (i.e. not only the validity of its blood pressureregulating effect by the production of angiotensin II (Ang II), but also the benefits beyond blood pressure lowering provided by agents that inhibit ACE activity) has been reported.1,2 ACE2 is another type of ACE, and the findings of this molecule as an Ang II breakdown enzyme indicate that a new therapeutic strategy for blood pressure regulation may be developed. 3 The recent studies of ACEs indicated the mechanisms for the regulation of gene expression, 4 localization, 5 and the presence of homologues 6 as well as multiple transcripts. However, the physiological and pathological functions of local ACE2, especially in human endothelial cells, and the effect of Ang II and/or pressure stress have not been well characterized.Recently, we reported that a particular type of mechanical stress, a pulsatile atmospheric pressure produced by an original pure pressureloading apparatus, has a cell proliferating effect and modulates the activities of cell-surface ACE in human aortic smooth muscle cells. 8In the present study, we used this device to show the effect on the expression of ACE2 and the localization of ACE2 in human aortic endothelial cells (HAEC) when cells were exposed to pulsatile-mechanic...