Bupivacaine and lidocaine blockade of calcium-mediated slow action potentials in guinea pig ventricular muscle.

The effects of bupivacaine and lidocaine on the slow-rising action potentials, induced by superfusion with high-K+ (26 mM) Tyrode's solution with 10(-6) M isoproterenol, were studied in guinea pig ventricular muscle. The concentrations of bupivacaine or lidocaine necessary to result in a 50% depression of the maximum upstroke velocity were about 10(-5) and 10(-4) M, respectively. The concentrations necessary to completely block the slow action potentials were about 10(-4) M for bupivacaine and 5 X 10(-4) M for lidocaine. The relative potencies of lidocaine to bupivacaine in abolishment of the slow action potentials are in the ratio of 1:5. These results suggest that local anesthetics do affect the slow Ca++ channel of ventricular muscle.