Effects of muscle stretch on transmitter release at end-plates of rat diaphragm and frog sartorius muscle.

1. Miniature end-plate potentials (m.e.p.p.s) and end-plate potentials were recorded intracellularly at neuromuscular junctions of the frog sartorius muscle and the rat diaphragm before, during and after muscle stretch.2. Stretch increased the frequency of the m.e.p.p.s and the mean quantum content (m) at end-plates of the sartorius muscle.3. Stretch enhanced m.e.p.p. frequency of the sartorius muscle in normal Ringer solution as well as in solutions high in magnesium and low in calcium content. In addition, an increase in frequency occurred in the presence of tetrodotoxin and in the absence of neostigmine methylsulphate.4. The magnitude of the increase in m.e.p.p. frequency in the sartorius muscle was negatively correlated with the control frequency.5. In contrast to the above findings at sartorius end-plates, muscle stretch did not affect the frequency of m.e.p.p.s or the m values at end-plates of the rat diaphragm.