Abstract
Changes produced in the excitability of muscle fibers were investigated by the use of the sartoris muscle of Bufo vulgaris fixed in a separating box, comparisons being made between the two kinds of V-t curves, namely, one obtained by the stimulation of the aneural portion and the other obtained when the transmission of impulse from the nerve to the muscle had been disconnected by the effect of end-plate blocking agents such as d-tubocurarine or procaine.
Besides, records of the end-plate potential and the accompanied action potential of the muscle were taken when the end-plate blocking was incomplete.
As the result of this investigation, this author could elucidate that there exists the relationship of the empirical formula of Weiss between the end-plate potential and the time elapsed from the appearance of the end-plate potential to the appearance of the action potential of the muscle and could offer an experimental support to the theory to say that the stimulation of the muscle by the local current caused by the end-plated potential is the last stage of the impulse transmission at the end-plate. In addition, the V-t curve determined after application of the blocking agent was found to shift upward proving that the excitability of the muscle itself is lowered by the application of the blocking agent.
When CaCl2 is applied on the muscle, the end-plate potential becomes extremely high while the impulse transmission becomes greatly disturbed. This fact was also proved experimentally to be due to the lewering of the excitability of the muscle fiber by the presence of an excessive amount of CaCl2.
In view of the findings stated above, it was concluded that a part of the mechanisms of the end-plate blocking agent is undoubtedly due to the lowering of the end-plate potential but the lowering of the excitability of the muscle fiber itself is also playing an important role in the appearance of the blocking effect of the end-plate blocking agent.
