Abstract
1. Amphibians of three genera; Amphiuma, Necturus, and Triturus ventricular muscle fibers were studied. The shape of the heart action potential was not independent of the size of the tissue masses.
2. With the effect of tissue size on the shape of the heart action potential, the large tissue masses and small tissue masses yield plateau as well as spikes. The plateau-shaped action potential was mainly recorded from the larger tissue masses.
3. The hypertonic solution of NaCl, CaCl2, MgCl2, glucose and (NH4) 2Ac produced the conversion of plateau to spike, in such as a similar mode on the dissection effect.
4. The effect of a Ca-removal agent, of EDTA, Na2C2O4 and (NH4) 2C204, produced to convert from plateau to spike in large tissue masses, and convert from spike to long lasting plateau-shaped in sliced small tissue masses.
5. The resting membrane-resistance increased during the application of certain hypertonic solution, the value of relative membrane resistance depended upon the concentration of certain agents, such as, applying high concentration produced to result a high relative membrane resistance. These measured resistances might be lumped resistances.
6. The hypertonic solution would make injuries by a toxic effect of certain agents. The injured areas might depend upon the concentration of applying agents, so that the situation on the effect by agent might be the same as a dissection.
7. The plateau-shaped action potential could separate several complexes mostly as a spike and plateau complex. The result was interpreted: the long duration of the excited state was the result of the fusion of discrete discharges of short duration as a subspike electrotonic potential and or spike potential.
8. Increased stimulus strength induced from the subspike or spike potential to larger plateau-shaped action potential, this unusual phenomenon might only be explained by the increasing of the population of excited cells.
