FACTORS DETERMINING THE TYPE OF RESPONSE IN THE FIBER OF STRIATED MUSCLE

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Abstract
Responses of a single fiber in a fresh preparation of the frog''s retro-lingual membrane were always maximal even when electrodes as small as 0.25 to 4.00 [mu] were used. Absence of circulation, injury, incident contractures, and age of preparation are conditions favorable for local graded contractions. A fatigued fresh fiber will give local responses. 30 stimuli per minute gave maximal responses even after 2 hrs. continuous stimulation: 33 stimuli per min. soon caused local contractions. The time necessary for their appearance shortened with the age of the preparation and with increase in frequency of stimulation above the minimum of 33 per min. A fiber responding locally to a given strength of stimulus may also respond in an all-or-none manner to the same stimulus. If a fiber is responding locally, the local contractions can be elicited with a coarse electrode (200 [mu] diameter). Fibers of a fresh preparation which had been responding only in an all-or-none manner gave local contractions when the Ringer was modified by addition of 0.028 g. KCl per 100 cc. Such contractions, as well as those obtained from fibers of an old preparation, were eliminated (with reversion to the all-or-none type) by changing the solution for Ringer plus 0.33 g. NaCl per 100 cc. This effect was reversible. The above change did not eliminate local contractions obtained from a fatigued or injured fiber. These results were also obtained with fibers of curarized preparations. It is concluded that the appearance of local contractions is dependent on the condition of the fiber and not on the size or mode of application of the stimulating electrodes.

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