Factors Influencing Facilitation in Actinozoa. The Action of Certain Ions

Abstract

1. The anaesthetic effects of carbon dioxide and magnesium added to sea water on Calliactis parasitica and Metridium senile have been studied. Magnesium first paralyses sense organs, but the main effect of both magnesium and carbon dioxide is a depression of neuromuscular facilitation. This prevents conduction of nervous impulses to the muscles in a way analogous to curarization of vertabrate skeletal muscle. 2. The chief effects of excess calcium, potassium and the hydrogen ion are increases in the size of the facilitated response to stimulation. The responses under potassium and the hydrogen ion are greatly prolonged and resemble the veratrine contracture of vertebrate skeletal muscle. 3. All the substances studied exert their chief effects at the neuromuscular junction. Analysis of their mode of action indicates that neuromuscular transmission in anemones involves two distinct processes, a process of excitation and a process of sensitization of the neuromuscular junction without which excitation of the muscle by the nervous impulse cannot be effective. This view is confirmed by examination of the relation of the size of the responses in normal animals to successive stimuli. The nature of the sensitization process and of the excitation process is discussed.