Electrotonic spread of current in cultured chick heart cells.

Following trypsin dispersion, isolated single cells reassembled into monolayer communities categorized as strands and sheets. Two microelectrodes were mounted in bridge circuits so that current pulses could be passed through one electrode while simultaneously recording membrane potentials at both electrodes. The electrotonic spread of current was measured as a change in membrane potential (usually at electrode 2) at various distances from the site of current injection (usually at electrode 1). Most cells were driven by transmission of excitation from contiguous cells. Criteria which helped to determine when both electrodes impaled the same cell included: (a) a sharp diminution of the resting potential recorded by the first electrode to a common intermediate level following insertion of the second electrode and (b) simultaneous and congruous subthreshold changes in membrane potential. The voltage/current relationship measured at electrode 1 was linear and had a mean slope of about 7 MΩ that for electrode 2 was also linear and, in some cases at short distances, had a slope as large as that for 1, i.e., the degree of electrotonic interaction was nearly 100%. However, in other impalements at short distances, interaction was nearly zero. Therefore, the degree of electrotonic spread was not dependent upon interelectrode distance per se, but appeared to depend on whether both electrodes impaled the same cell.