A comparison of in vitro cellular responses to mechanical and electrical stimulation

In the last several decades, enormous interest has been generated toward understanding the cell as it is controlled by its external physical environment. The purpose of this study was to determine the effects of well-defined applied mechanical stress and time-varying electric fields on the cellular synthesis of connective tissue macromolecules. Chondrocytes harvested by trypsin digestion of 15-day-old chick embryo sternae were randomly dispersed and cultured on elastin membranes in a humidified atmosphere with 10 per cent CO2 and 90 per cent air. Following five days of growth in F12 media and 5 per cent fetal calf serum, the membranes underwent either 1) a 10 per cent cyclic mechanical stretch or 2) 60 Hz A.C. electrical stimulation with current densities of 1 to 1,000 nA/mm2 or 3) control without stimulation, each for an eight-hour period. C14-hydroxyproline incorporation into collagen, and H2 35 SO4 incorporation into glycosaminoglycans (GAGs) were measured by liquid scintillation techniques. Scanning and transmission electron microscopy analysis of control and stimulated cells demonstrated discernable differences. Both mechanically and electrically stimulated chondrocytes showed a two- to three-fold increase in GAG synthesis and a general depression in protein and collagen synthesis over controls. The general similarity in response to both mechanical and electrical stress suggests common processes by which they modulate cellular synthesis of cartilage connective tissue proteins.