The effect of muscle contraction on the regulation of adenosine formation in rat skeletal muscle cells.

1. The present study examined the effect of muscle contraction on the rate of extracellular adenosine formation and on the distribution of 5' nucleotidase in primary rat skeletal muscle cells in culture. Experiments were also performed to determine whether the muscle cells release a metabolite upon contraction which may influence the extracellular production of adenosine. 2. Muscle contraction, induced by electrical stimulation, increased (P < 0.05) the rate of adenosine formation in the presence of physiological concentrations (2 and 5 microM) of adenosine monophosphate (AMP). Muscle contraction also led to an increase (P < 0.05) in the maximal rate of extracellular adenosine formation from 4.09 +/- 0.19 to 7.04 +/- 0.27 micromol (g protein)-1 min-1. Similarly, homogenates of contracted muscle cells had a higher (by 19.5 +/- 10.5 %; P < 0.05) AMP 5' nucleotidase activity than homogenates of control cells. 3. Addition of buffer from contracted cells to control cells induced an elevation (18.4 +/- 5.3 %; P < 0.05) in the rate of adenosine formation. The rate of adenosine formation was also increased with decreased intracellular adenylate charge (P < 0.05). 4. Cell homogenates treated with detergent had a higher (by 58.0 +/- 16.3 %; P < 0.05) AMP 5' nucleotidase activity than untreated homogenates, suggesting the existence of an enclosed pool of 5' nucleotidase within the muscle cells. The rate of adenosine formation in the detergent-treated homogenates was similar for electrically stimulated and non-electrically stimulated cells. 5. The present data show that muscle contraction induces an enhanced extracellular adenosine production via an increase in the activity of ecto AMP 5' nucleotidase. The activity of 5' nucleotidase can be elevated via a compound released by muscle cells during contraction and by alteration in intracellular adenylate charge. It is furthermore proposed that the extracellular adenosine formation is increased by translocation of 5' nucleotidase from an enclosed intracellular pool to the muscle membrane.