CALCIUM RESPONSES OF ENDOTHELIAL-CELL MONOLAYERS SUBJECTED TO PULSATILE AND STEADY LAMINAR-FLOW DIFFER

The vascular endothelium is the primary transducer of hemodynamically imposed mechanochemical events. In this study, we measured the intrace llular free calcium concentration ([Ca2+](i)) using the fluorescent pr obe fura 2 and ratiometric digital imaging in cultured bovine aortic e ndothelial cells (BAEC) subjected to various laminar flow patterns. Th ese were steady shear stress (0.2-70 dyn/cm(2)) and three types of sin usoidal pulsatile shear stress (nonreversing: 40 +/- 20 dyn/cm(2); rev ersing: 20 +/- 40 dyn/cm(2); and purely oscillatory: 0 +/- 20 dyn/cm(2 ); flow frequencies: 0.4, 1.0, and 2.0 Hz) in a serum-containing mediu m. The most dramatic finding was failure of a purely oscillatory flow to increase [Ca2+](i) in BAEC monolayers. In contrast, steady flow, as well as nonreversing and reversing pulsatile flows, increased [Ca2+]( i). The dynamics of the response were dependent on the flow pattern. B oth internal Ca2+ release and extracellular Ca2+ entry were involved i n these [Ca2+](i) increases. Also, switching from either a steady nonr eversing pulsatile or reversing pulsatile flow back to a static condit ion resulted in a [Ca2+](i) increase. However, switching from an oscil latory flow to a static condition did not induce any changes in averag e [Ca2+](i). This study shows that endothelial cells are able to sense different flow environments in terms of [Ca2+](i) signaling and is re levant to further studies of the influence of hemodynamic forces on va scular pathophysiology.