In vitro system to study realistic pulsatile flow and stretch signaling in cultured vascular cells

We developed a novel real time servo-controlled perfusion system that exposes endothelial cells grown in nondistensible or distensible tubes to realistic pulse pressures and phasic shears at physiological mean pressures. A rate-controlled flow pump and linear servo-motor are controlled by digital proportional-integral-derivative feedback that employs previously digitized aortic pressure waves as a command signal. The resulting pressure mirrors the recorded waveform and can be digitally modified to yield any desired mean and pulse pressure amplitude, typically 0-150 mmHg at shears of 0.5-15 dyn/cm². The system accurately reproduces the desired arterial pressure waveform and cogenerates physiological flow and shears by the interaction of pressure with the tubing impedance. Rectangular glass capillary tubes [1-mm inside diameter (ID)] are used for real-time fluorescent imaging studies (i.e., ph(i), NO, Ca²⁺), whereas silicon distensible tubes (4-mm ID) are used for more chronic (i.e., 2-24 h) studies regarding signal transduction and gene expression. The latter have an elastic modulus of 12.4.10⁶ dyn/cm² similar to in vivo vessels of this size and are studied with the use of a benchtop system. The new approach provides the first in vitro application of realistic mechanical pulsatile forces on vascular cells and should facilitate studies of phasic shear and distension interaction and pulsatile signal transduction.