The vascular endothelium is the primary transducer of hemodynamically imposed mechanochemical events. In this study, we measured the intracellular free calcium concentration ([Ca2+]i) using the fluorescent probe fura 2 and ratiometric digital imaging in cultured bovine aortic endothelial cells (BAEC) subjected to various laminar flow patterns. These were steady shear stress (0.2-70 dyn/cm2) and three types of sinusoidal pulsatile shear stress (nonreversing: 40 +/- 20 dyn/cm2; reversing: 20 +/- 40 dyn/cm2; and purely oscillatory: 0 +/- 20 dyn/cm2; flow frequencies: 0.4, 1.0, and 2.0 Hz) in a serum-containing medium. 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. Both internal Ca2+ release and extracellular Ca2+ entry were involved in these [Ca2+]i increases. Also, switching from either a steady nonreversing pulsatile or reversing pulsatile flow back to a static condition resulted in a [Ca2+]i increase. However, switching from an oscillatory flow to a static condition did not induce any changes in average [Ca2+]i. This study shows that endothelial cells are able to sense different flow environments in terms of [Ca2+]i signaling and is relevant to further studies of the influence of hemodynamic forces on vascular pathophysiology.
- Copyright © 1995 the American Physiological Society