Propionic Acid Reversibly Enhances Synaptic Depression During Tetanic Stimulation Of The Crayfish Neuromuscular Junction

Abstract

Endocytosis and exocytosis are both integral components of synaptic communication between neurons and the cells they innervate. Exocytosis allows for the release of neurotransmitters. Endocytosis plays a role in membrane recycling, retrieving membrane that fused with the presynaptic membrane during transmitter release. The processes involved in endocytosis are complex and have not yet been completely elucidated. The development of a technique to separate the processes of endocytosis and exocytosis in the crayfish neuromuscular junction would be an invaluable tool in the study of neuronal communications. This paper considers intracellular acidification of the crayfish neuromuscular junction as a way of separating these two closely linked processes. Preparations were made in which the interior of the cell was acidified by propionic acid, a method of blocking endocytosis, but not exocytosis, demonstrated in the lizard neuromuscular junction (Lindgren et al. 1997). The preparations were subjected to tetanic stimulation in order to produce depression. Acidification produced a marked enhancement in depression of excitatory junction potential activity. This depression was partially reversible upon cessation of stimulation and fully reversible upon removal of acid from the preparation.