Monophasic Action Currents from the Uninjured Turtle Ventricle

Abstract

Monophasic action currents obtained by derivation from 2 uninjured points on heart muscle have often been mentioned in the literature. Samojloff, 1 for example, produced a block by transverse cutting or compression of the frog heart and recorded monophasic action currents by derivation from uninjured base and apex. In this experiment, however, the apical muscle constitutes an extension of the lead to the injured surface. DeBoer 2 has recently stressed his observation that, employing base-apex leads in the frog, the weak beat in alternation may be associated with monophasic action currents. Although no injury was produced in these experiments by mechanical means, the blocking of the impulse must have been due to the presence of muscle in an abnormal physiological state. Gilson 3 has recorded monophasic action currents following injury, but at a time when the demarcation current had shrunk practically to zero.

In our observations, which are incidental to a study of the action currents of the turtle heart, monophasic action currents were produced as follows. The whole heart was excised. A thread was tied to the frenum, care being taken not to injure the apex. Threads were attached to the great arteries, which were cut near the ventricle, and to the apex of each auricular appendage. Each of the 3 threads, excluding that at the frenum, was tied to a very thin strip of rubber elastic by which the heart was suspended from a rod. The heart was partly lowered into a small beaker. The apical thread was then passed under a hook attached to the floor of the beaker by cardboard and paraffin, and fixed outside the beaker. Thus, on contraction, the base of the heart was drawn down, and the apex was relatively immobile.