Bioassay development: The implications of cardiac myocyte motility in vitro

Cardiac myocytes cultured over microfabricated extracellular recording devi ces can be used to assay bioactive compounds. However, electrophysiological signals recorded from these devices vary in amplitude with time. Theoretic ally, changes in signal amplitude arise from myocytes being moved over reco rding sites by cocultured fibroblasts. To test this, neonatal rat cardiac m yocytes were cultured at high densities and low densities on fibronectin-co ated glass. After 36.5 h, myocytes were identified Ly their rhythmic contra ctions and then time-lapse-recorded for 3.5 h. Length, width, and angle of orientation was then determined every 30 min for five cells in low density and five cells in high-density culture. Low-density cells had mean lengths of 65.3 mu m and widths of 35.1 mu m, whereas cells in high-density culture had greater mean lengths of 74.2 mu m and lower mean widths of 24.3 mu m. Length, width, and angle of orientation of cells in low- and high-density c ulture changed LS; 4.1%, 11.8%, and 2.7 degrees, and 6.4%, 10%, and 4.6 deg rees, respectively, every half hour. We found no evidence of myocyte-fibrob last interactions influencing cell position or shape in low density, hut in high density, we found evidence that fibroblast-myocyte interactions could transiently influence cell shape. We conclude that fibroblast-independent changes in cell shape are largely responsible for the changes in signal amp litude recorded from cardiac myocytes cultured on microfabricated extracell ular recording devices. However, there is some evidence that myocyte-fibrob last interactions may augment this process in high-density culture. The imp lications of these findings for bioassay development are discussed.