Interaction of lidocaine and calcium on the electrical characteristics of rabbit atria

The interactions of lidocaine (1-5 x 10^-5M) and calcium ions (1.25-5.0 mM) on electrical characteristics of atrial potentials were determined with standard microelectrode techniques with major reference to the maximum rate of rise of the action potential (V(max) of AP), the time constant of recovery of the rapid sodium carrier and repetitive firing due to early extra stimuli (arrhythmia). Lowering Ca caused depolarization and decreased V(max) and Υ; high Ca caused changes in the opposite direction. The relation of Υ to membrane potential was downward concave when membrane potential was changed by Ca but upward concave when equivalent changes in membrane potential were induced by changing the external potassium concentration. Lidocaine (1 x 10^-5M) had no significant effect at 2.5 mM Ca but significantly decreased the overshoot and V(max) of AP, increased Υ and effective refractory period and was antiarrhythmic at 1.25 mM Ca. These changes were closely similar to the effect of lidocaine (5 x 10^-5M) at 2.5 mM Ca. The effects of this high concentration were decreased when Ca was changed to 5.0 mM. The effect of lidocaine most clearly predictive of efficacy for the type of arrhythmia was that on V(max), with changes in Υ in particular not being related to antiarrhythmic activity.