EFFECTS OF CA+ AND K+ ON OSCILLATORY AFTERPOTENTIALS IN DOG VENTRICULAR MUSCLE-FIBERS

Oscillatory afterpotentials were observed in dog ventricular muscle fibers at normal resting potential levels. These oscillatory afterpotentials appeared in the K+-free, high-Ca2+ solutions containing 3.5 mm Ca2+ or higher and followed the train of applied impulses. The amplitude of the oscillatory afterpotentials was dependent upon the external Ca2+ concentration. The oscillatory afterpotentials became larger by the application of isoproterenol (4 × 10-7 m) and a low concentration of caffeine (1 mm) but a high concentration of 5 and 10 mm, stopped the oscillatory afterpotentials. The application of verapamil (1 or 4 × 10-6 m) suppressed the oscillatory afterpotentials but took more than 20 min to achieve a complete abolition of these activities. The oscillatory afterpotentials were associated with tension development. Mild reduction of the external Na+ to 75% of the control increased the oscillatory afterpotentials, but further reduction suppressed them. The addition of 2.7 mm K+ or Rb+ in the perfusing medium easily stopped the oscillatory afterpotentials. In the presence of a lower concentration than 2.7 mm, both the K+ and the Rb+ showed concentration-dependent suppression of the oscilatory afterpotentials and the effects were similarly observed at the same concentration of each ion. The threshold to stop the oscillatory afterpotentials was found to be at a concentration between 1.08 and 1.35 mm using both K+ and Rb+. These results suggest that increased internal Ca2+ and/or reduced K+ conductance have an important role in the appearance of the oscillatory afterpotentials. © 1979.