Tetrodotoxin-sensitive component in action potential plateau of guinea pig Purkinje fibers: Comparison with the papillary muscle

Abstract

1. The effects of tetrodotoxin on action potentials of isolated guinea pig Purkinje fibers were examined and compared the findings with those obtained in the ventricular papillary muscle, by use of conventional microelectrode techniques. 2. Tetrodotoxin (5 × 10 −7–10 −5 M) decreased the amplitude, overshoot, and maximum upstroke velocity of action potentials of the Purkinje fibers, and shortened the duration of action potential at all levels of repolarization concentration- and stimulus cycle length-dependently. 3. The longer the stimulus cycle length, the greater the shortening by the drug of the action potential duration. 4. In particular, the plateau potential of the Purkinje fibers exposed to tetrodotoxin was remarkably depressed, and which occurred even in case of blockade of K + conductance, using tetraethylammonium. 5. On the other hand, a high concentration (10 −5 M) of tetrodotoxin did not significantly affect the papillary muscle action potentials. 6. These findings suggest that there is a tetrodotoxin-sensitive component of Na + current in plateau voltage range of the Purkinje fibers, but little in the papillary muscle, and that the component plays an important role to maintain the plateau of Purkinje fibers action potential.