Intracellular Potentials in Rat Atria during and after Vagal Stimulation or Acetylcholine Administration

RECENTLY, Vaughan Williams 1 observed that the shortening of the duration of the intracellularly recorded action potential in rabbit atria following vagal stimulation or acetylcholine administration is not always associated with diminished atrial contractions. In fact the association between the two phenomena as observed by Burgen and Terroux 2 might be coincidental. The question arose whether the slowing-up of the atrium which will result from vagal stimulation or acetylcholine administration is always connected with a shortening of the duration of the atrial action potential. The right atrium of adult Wistar rats was impaled with glass micro-electrodes filled with 3 M potassium chloride, their tip diameter being < 0.5μ and their resistance 20–35 MΩ. After retrograde insertion of a plastic cannula in the thoracic aorta, the heart and both vagi were perfused in situ with normal Tyrode solution. The vagi were stimulated with rectangular current pulses of varying intensity. The pulses had a frequency of 10 c./sec. and a duration of 0.5 m.sec. In a few experiments we succeeded in recording intra-cellular atrium potentials from artificially ventilated animals that had an intact circulation. The results obtained with perfused rats and with rats with an intact circulation did not differ.