Small signal impedance of heart cell membranes

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Abstract
The electrical impedance of seven-day ventricular embryonic chick heart cell membranes maintained in tissue culture was measured under voltage clamp using the two-microelectrode voltage-clamp technique. Small sinusoidal perturbations were added to the voltage-clamp potential and the amplitude and phase of the steady-state sinusoidal response in current was recorded as a function of mean clamp potential or perturbing frequency. The experimental results are compared with two models of excitability for heart: the MNT model (McAllister, Noble & Tsien,J. Physiol. (London) 251:1–59, (1975) and the BR model (Beeler & Reuter,J. Physiol. (London) 268:177–210, 1977). The small signal impedance of heart cell membranes, in theory and experiment, shows a resonance near 1 Hz and near the threshold potential. The effect of this resonance is to increase the effective length constant of the membrane for these conditions.