Effect of glycerol treatment on transmitter release at the frog neuromuscular junction

Exposure of frog skeletal muscle to a Ringer solution made hyperosmotic with glycerol, followed by return of the preparation to a normal Ringer, results in an irreversible uncoupling of the mechanical activity of the muscle. This technique for preventing muscle contraction has often been used to study neuromuscular transmission under normal or high levels of release without interference from muscle contraction. Little was known, however, about the effects of glycerol treatment on the process of transmitter release. In this paper we report the results of a study in which we examined the effects of glycerol treatment on transmitter release during repetitive stimulation at the frog sartorius neuromuscular junction. We found that glycerol treatment altered the stimulation-induced changes in end-plate potential (EPP) amplitude normally observed during repetitive stimulation at this synapse. This effect, which increased progressively with time for up to 8 h following removal of glycerol, could be accounted for by presynaptic changes in the amount of transmitter released.