MECHANICAL RESPONSES GENERATED BY ALTERNATING CURRENT OR REPETITIVE SQUARE PULSES IN THE FROG SKELETAL MUSCLE

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  • 真島 英信
    Department of Physiology, School of Medicine, Juntendo University
  • 土屋 尚子
    Department of Physiology, School of Medicine, Juntendo University

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1. The mechanical response of frog's semitendinosus muscle generated by AC or SP at various frequencies and intensities were studied, referring to the electrical changes in membrane potential described in the previous paper.<BR>2. The AC stimulation generated the early tetanic contraction due to propagating spike potentials and the late contracture response due to non-propagating local responses. Both the early and late contractions were separated when the longitudinal AC between 200-1000c/sec was applied.At the frequency higher than 500c/sec the early contraction became a twitch.In the strong transverse AC field the late contraction was dominant and it was decreased at more than 2000c/sec.<BR>3. In the excess potassium (9-18mM) solution the early contraction was abolished.<BR>4. Both contractions were decreased by the sodium removal or the presence of 10-8g/ml tetrodotoxin.<BR>5. The effect of SP stimulation was similar to that of AC and the difference in the frequency characteristics was explained by the difference of electrical changes.<BR>6. In the sodium-free solution, strong AC or SP evoked some tension, which was decreased with increasing frequency.Transverse AC was more effective than SP at less than 200c/sec but the effect was reversed at more than 200c/sec.<BR>7. Raising the external calcium concentration, the late contraction in the excess potassium or sodium deficient solution was augmented.<BR>8. In the chloride-free solution the late contraction was augmented and the relaxation was slowed.

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