Action potential of insect muscle examined with intra-cellular electrode.

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(1) The nature of the action potential of the insect muscle was investigated, using the method of intracellular recording. The materials used were the wing muscles of a locust (Locusta migratoria danica). Sometimes the sound muscles of cicadas (Graptopsaltria nigrofuscata and Platypleura kaempferi) were also employed.(2) The insect muscle fiber showed a low resting potential which ranged.between 40 and 60 mV. The potential depended upon the extracellular concentration of potassium.(3) The average space constant of the muscle fiber was 0.6 mm. and the.average time constant was 8.5 m. seconds.(4) The action potential ranged between 30 and 50 mV and did not show any obvious overshoot.(5) The latent period of the action potential was approximately constant at every point of the muscle fiber. From this fact the presence of the distributed nerve ending was concluded.(6) In direct electric stimulation the first group of fibers responded with pure electrotonic potentials, the second group with local potentials and the third with all or none spikes. Most fibers belonged to the second group.(7) The size of the action potential was varied over a wide range by increasing (sometimes by decreasing) the resting membrane potential with anodic (sometimes with weak cathodic) polarization. The action potential and the resting membrane potential were in general found to be approximately proportional, and in only few cases the action potential became larger than that expected from the proportional relation.(8) The time constant of the decay of the action potential was about 5, msec. which was smaller than that of the resting muscle membrane. The difference seems to be due to the increase of the potassium leakage.(9) Some effects of tetra-ethyl-ammonium chloride, of tetra-buthyl-ammonium chloride and of choline chloride on the insect muscle were investigated.(10) The resting and action potential of the sound muscle of cicada were almost similar to those of the wing muscle of the locust. But in some condition the action potential of the sound muscle of Platypleura kcaempferi showed an obvious overshoot as well as an obvious step which indicated a transition from the local to the propagative potential.(11) From the above results it is concluded that in the wing muscle of the locust the major component of the action potential is a nonselective ion sink analogous to the end plate potential of the vertebrate muscle, and the potential analogous to the propagative potential of the vertebrate, even if it exists, does not generally play an important role. But in some other muscles such as the sound muscle of Platypleura kaempferi the latter potential plays much more important role than in the wing muscle of the locust.