Abstract
Choline acetylase is present in rabbit atria and forms acetylcholine continuously. It is known that the contractions of isolated atria cease when the temperature falls to a point below 20 degrees C., and that they can be started again by acetylcholine, which causes a rise in the transmembrane potential. The question may therefore be asked whether the transmembrane potential is normally kept sufficiently high for impulses to be propagated by the acetylcholine which is formed within the atria. The effect of lowering the temperature on choline acetylase activity has therefore been studied. The activity was found to decline much more steeply below 20 degrees C. than between 33 degrees and 20 degrees . The Q(10) rose to 7.8. This finding is consistent with the view that one function of choline acetylase activity is to maintain the transmembrane potential.