Concentration dependence of the veratrine effect on inducing depolarization and membrane potential oscillation in...

The concentration dependence of the effect of veratrine in inducing depolarization and membrane potential oscillation in the frog sartorius muscle has been studied. (1) On increasing the veratrine concentration from 0.025 to 1 mM, the latency period of the development of membrane potential oscillation and depolarization is proportionally shortened. (2) On changing the veratrine concentration from 0.025 to 1 mM, the magnitude of depolarization is raised logarithmically. (3) When the veratrine concentration reaches 0.05-0.1 mM, both the amplitude and the frequency of the membrane potential oscillation increase. On rising to 1 mM, a further increase in frequency to eight-fold occurs especially in the later phase of oscillation. At this concentration range, the amplitude of oscillation inversely proportional to the concentration of veratrine. (4) On increasing the veratrine concentration above 0.1 mM, the membrane potential oscillation ceases after a temporary rise of frequency. This inhibitory effect of veratrine is, however, reversible, and oscillations appear again, despite the absence of veratrine in Ringer's solution. This also proves the persistance of the veratrine effect.