Electrical activity of sinoatrial node cells of the rabbit surviving a long exposure to cold Tyrode's solution

The right atrium including the sinoatrial node was excised from the rabbit heart, immersed in Tyrode's solution, and kept at 0-3 degrees C for several days. The tissue then was warmed to 36-37 degrees C in well oxygenated Tyrode's solution. Transmembrane potentials from cells in the sinoatrial node region and the right atrium were recorded with microelectrodes. After 3 days of storage, the maximum diastolic potential of cells in the sinoatrial node region decreased, but the configuration of the action potential was identical to that of the pacemaker pacemaker potential in the fresh preparation. After 5-7 days of storage, the sinoatrial node tissues in some preparations showed well preserved membrane potentials and pacemaker activity, while in others, the cells were electrically quiescent, or showed subthreshold oscillatory potentials of low amplitude. Transmembrane potentials could not be recorded from the right atrial tissue after storage for this period. Sinoatrial node action potentials with normal configuration were recorded from preparations stored for longer than 10 days. The sinoatrial cells in these preparations responded well to norepinephrine and acetylcholine, indicating that the reactivity of receptors was well preserved. The results provide electrophysiological evidence that cells in the sinoatrial node region can withstand long exposure to cold and retain their sensitivity to neuromediator action, but atrial myocardial cells cannot.