RESUMPTION OF CONTRACTIONS AFTER FREEZING IN LIQUID NITROGEN IN SMALL PIECES OF RAT HEART CONTAINING PACEMAKING CENTERS

The investigation reported in this paper represents an attempt to repeat with the rat heart experiments previously conducted with the frog heart, in which small pieces cut from the upper part of the organ and selected for their ability to undergo spontaneous rhythmic contractions (that is, pieces containing pacemaking centers) survived freezing in liquid nitrogen. Pieces measuring 1 to 2 mm on the side, cut from the atria and the septa of rat hearts, and observed to beat spontaneously were exposed for 1.5 min in Eagle's medium containing 20% ethylene glycol, then frozen in liquid nitrogen and thawed rapidly in Eagle's medium at room temperature. Out of 54 pieces so treated, 24 (44%) resumed rhythmic contractions spontaneously and continued beating for hours, occasionally up to 40 hrs, at room temperature. Recovery from the injury inflieted by dissection alone required some 15 min to 2 hrs; recovery from exposure to ethylene glycol, a few minutes; and recovery from the freezing-thawing ordeal, 30 min to several hours. © 1969.