Effects of Low Temperatures on Transmembrane Potentials of Single Fibers of the Rabbit Atrium

Abstract

Lowering the temperature caused a fall in the diastolic membrane potential and action potential and an increase in the duration of the action potential in both pacemaker and nonpacemaker fibers of the rabbit atrium. Pacemaker fibers were the most resistant to cooling and continued to discharge at a temperature where all conducted action potentials and mechanical contractions had ceased. Acetylcholine (10 -7 Gm./ml.) administered at a low temperature when only pacemaker fibers were discharging, elicited propagated action potentials and contractions. This effect was associated with an increase in diastolic membrane potential towards that existing at a temperature of 30 C.