Journal of Applied Physiology
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J Appl Physiol 73: 71-74, 1992;
8750-7587/92 $5.00
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Journal of Applied Physiology, Vol 73, Issue 1 71-74, Copyright © 1992 by American Physiological Society

ARTICLES

Aminophylline increases submaximum power but not intrinsic velocity of shortening of frog muscle

B. M. Block, S. R. Barry and J. A. Faulkner
Department of Physiology, University of Michigan, Ann Arbor 48109.

We hypothesized that methylxanthines, such as aminophylline, increase the power developed by submaximally activated frog skeletal muscles by increasing the force developed at any given velocity of shortening. Frog semitendinosus muscles were excised and tested at 20 degrees C in oxygenated control and aminophylline Ringer solutions. Force-velocity relationships were determined and power was calculated from muscles stimulated at frequencies of 80 and 300 Hz. The 300-Hz frequency of stimulation produced a maximum rate of force development. In 50 and 500 microM aminophylline, twitch force increased by 25 +/- 12 and 75 +/- 13%, respectively. Aminophylline did not affect maximum isometric force generation or the shortening velocity at any relative load. At 80-Hz stimulation and in the presence of 500 microM aminophylline, power increased by an average of 11% at 10 of 14 relative loads. At maximum frequencies of stimulation, aminophylline had no effect on any measured parameter. We conclude that aminophylline increases the power developed by submaximally activated frog muscles through an increase in the force generated particularly at the lower velocities of shortening.


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