THE POTENTIAL ANALYSIS OF A PACEMAKER MECHANISM IN LIMULUS POLYPHEMUS

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Abstract
Individual ganglion cells assumed to have pacemaker functions, or such cells in association with small groups of other cells, in the median cardiac nerve of L. polyphemus, show spontaneous activity when entirely separated from the body. During such activity the single ganglion cell, or such a cell in association with a small group of other cells, develops a sustained negative potential. During this period of sustained negativity there is a repetitive nerve fiber response. The sustained negative potential develops rather rapidly and then slowly subsides. There is no evidence of any appreciable positive after-potentials . Activity in the fibers develops during the rising phase of the sustained potential and continues throughout the greater part of the period of negativity. The fiber response is most rapid during the height of the sustained potential and is slower as it subsides. Strychnine, as an excitant, causes an increase in amplitude and duration of the sustained negative potential. The frequency of occurrence of the sustained negative potentials is increased, as is the frequency of the fiber response during each period of sustained potential. Acetylcholine, as a depressant, retards the frequency of development of the sustained negativity and lowers and shortens the potential. There is a diminution in the frequency and duration of fiber response. Adrenalin and cocain in concns. causing increased excitability cause changes in the sustained negative potential similar to those produced by strychnine. As a depressant cocain decreases the amplitude of the sustained negative potential to a greater degree than does acetylcholine for a corresponding degree of slowing of the frequency of its occurrence.

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