Fig. 4. Current injection experiments. (A ) A Purkinje strand impaled by three microelectrodes near one end used for current passing (Me¹) and recording electrotonically conducted voltage pulses (ΔV¹and ΔV²) as discussed in the text. (B ) The time course of epinephrine-induced simultaneous changes in conduction velocity (θ), linear conductance (S in fig. 4A) and rates of phase 0 depolarization by electronic differentiation (V^max) and rapid A/D sampling (V^maxf) in one experiment as a percentage of the control (time 0 value) just before exposure to epinephrine with 0.2 mm octanol. (C ) Solid black line = linear least squares fit to the equation θ²= V^maxf/R using the experimental data from (B ); dotted lines = linear correlation between changes in the active (V^maxf) and passive (conductance S) components of the approximate cable equation. (D ) Correlation between decreases of conduction velocity and intracellular (IC) diastolic threshold current in another Purkinje preparation exposed to epinephrine with 0.2 mm octanol.