THE RELEASE OF ACETYLCHOLINE FROM MAMMALIAN MOTOR NERVE ENDINGS

Abstract

The release of acetylcholine from rat and guinea-pig isolated diaphragm preparations stimulated through the phrenic nerve was optimal at 37° in Krebs solution with 5 × 10⁻⁶ neostigmine methylsulphate. The amount of acetylcholine released by a 20 min. tetanus was reduced by cooling. At frequencies of stimulation above 6/sec. the release was less than that predicted. This “failure” was unaffected by the addition of 1 × 10⁻⁶ choline. The acetylcholine release declined with continued stimulation at 25/sec. In the absence of nerve stimulation, there was a small continuous resting release of acetylcholine which seemed to originate in the muscle fibres. These results are discussed in the light of current electrophysiological knowledge of the quantal release of acetylcholine.