The effect of procaine on the passive electrical properties of guinea-pig ventricular muscle.

Electrotonic potentials produced by rectangular hyperpolarizing current pulses were recorded intracellularly at various distances from guinea-pig papillary muscles and the results were analyzed according to the single-dimensional cable model. In normal Tyrode solution the space constant (lambda) was 0.62 +/- 0.12 mm (mean and S.D., nine preparations) and the time constant (tau) was 4.0 +/- 0.8 ms. Procaine (1 mg/ml) increased lambda to 1.20 +/- 0.29 mm and tau to 19.7 +/- 4.7 ms by increasing the membrane resistance, while the membrane capacity was only slightly increased and little change was observed in the internal longitudinal resistance. The dose-response relationship revealed that procaine inhibited the resting membrane conductance almost completely in a one-to-one manner with the dissociation constant of about 1 mM. It was suggested that potassium conductance predominant in the resting membrane conductance in guinea-pig papillary muscle was depressed by procaine and that electrical coupling is well maintained even when the membrane resistivity of apposed normal ordinary membrane at intercalated disks becomes high.