Effect of Cooling on Neuromuscular Transmission in the Frog

¹ From the National Institute of Neurological Diseases and Blindness, National Institutes of Health, Bethesda, Maryland

Recording with intracellular electrodes from endplate regions of frogs sartorius muscle showed that at –1°C miniature endplate potentials still occurred and that the resting membrane potentials differed very little from those recorded at room temperatures. The miniature potentials, however, were decreased in frequency and increased in amplitude by cooling; and at about 5°C, the amplitude began to fall while the frequency continued to be low. It was also at about 5°C that the muscle responses to nerve stimulation frequently consisted of endplate potentials only. Upon rewarming spike potentials again appeared. These observations suggest that there is a critical temperature for neuromuscular transmission, below which impediment of impulse transmission began; and in the frog it is 5°C. The experiments also demonstrated that during the process of cooling a blockage of impulses at one neuromuscular junction and transmission across the other in a single muscle fiber could occur.