May 1, 1973

Effects of isoprenaline on contractions of directly stimulated fast and slow skeletal muscles of the guinea-pig

British Journal of Pharmacology
N Tashiro


1. The actions of isoprenaline on the contraction and the resting potential of the isolated extensor digitorum longus (EDL), a fast contracting muscle, and the soleus, a slow contracting muscle, of the guinea-pig were investigated. Twitch tension was elicited by direct supramaximal stimulation and recorded isometrically.2. The twitch tension of EDL elicited by pulses of 0.5-10 ms duration was increased in the presence of isoprenaline (1 mug/ml). Isoprenaline increased the twitch tension of the soleus elicited by a pulse of more than 5 ms duration, but decreased it when elicited by a pulse of less than 1 millisecond. These effects were blocked by propranolol (1-3 mug/ml) but not by phentolamine (1-5 mug/ml).3. In EDL, isoprenaline prolonged the time to peak tension and the half-relaxation time. The twitch of the soleus was shortened by isoprenaline due to an acceleration of relaxation. These findings were independent of stimulus duration.4. The potentiating effects of isoprenaline on the twitch tension of EDL and the soleus were not observed in K(+)-free Krebs solution and were abolished by ouabain (1 mug/ml) and by reduction of the temperature from 33 degrees to 18 degrees C. The effects of isoprenaline on the relaxation proces...Continue Reading

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  • Citations44


Mentioned in this Paper

Chloride Ion Level
Resting Potentials
Contraction (Finding)
Soleus Muscle Structure
LIPG protein, human
NOS Activity (Molecular Function)

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