Abstract
The effect of caffeine on the neuromuscular transmission was investigated by recording the end-plate potential (e. p. p.) of the frog sartorius muscle using an intracellular microelectrode.
2. Caffeine increased the e. p. p. amplitude. The threshold concentration was about 0.5-1×10-4g/ml. The amplitude of e. p. p. was 158±16 of control size in the presence of 3×10-4g/ml caffeine.
3. The quantum content was increased in the presence of 2×10-4g/ml and 2.5×10-4g/ml caffeine by factors of about 1.5 and 2, respectively.
4. The frequency of the miniature end-plate potential (m. e. p. p.) was in creased by about 3-fold with 3×10-4g/ ml caffeine without an appreciable increase of m. e. p. p. size.
5. The potentiating effect of caffeine became more marked when calcium concentration of the external medium was lowered, but the effect was usually transient when the calcium concentration was below 1/10 of the normal value.
6. After a train of stimuli at 50 Hz for 30 sec post-tetanic potentiation occurred in the presence of caffeine with the same time course as in the control Ringer's solution.
7. It is suggested that caffeine acts on the presynaptic nerve terminal and facilitates the release of calcium from the stored site within the nerve terminal.
