Electrophysiological properties of tissue cultured heart cells grown in a linear array

Embryonic chick heart cells were grown in tissue culture on an oriented substrate (channels cut in an agar coated slide), so that they formed narrow(5-100mu) strands of arbitrary length. The electrical properties of these strands were examined using intracellular microelectrodes. ac and dc cable studies were performed to determine the passive cable parameters. Quantitative histology, using light and electronmicroscopy, permitted calculation of intrinsic capacitances and resistivities. Electrical coupling between polarizing and recording electrodes was ubiquitous, falling off exponentially with distance. It was concluded that individual cells were electrically connected, since coupling was observed at distances greater than 3 mm, and the maximum cell length was estimated to be less that 300 mu. The strands were usually spontaneously active, with phase 4 depolarization (pacemaker potential) occurring almost simultaneously in all cells of a strand. The passive electrical properties determined during phase 4 were: core resistivity (cytoplasm plus cell-to-cell resistance), 245 ohm/cm; membrane capacitance, 1.46 muF/CM2. The membrane resistance increased from 16 to 136 kohm/cm2 during phase 4. The space and time constants showed commensurate changes, from 0.95 to 3.2 mm, and from 29 to 269 msec, respectively. The input resistance also increased, from 1.1 to 3.8 Mohm.