The exchange of 18O between water and phosphate compounds in isolated frog sartorius muscle under conditions of negative work
(1974) Journal of mechanochemistry & cell motility — Vol. 3, n° 1, p. 39-54 (1974)
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- Authors
Maréchal, Georges 
- Abstract
- Frog sartorius muscles were soaked at 0°C for 2 minutes in a Ringer solution enriched with H2 18O. Five minutes after the first contact with the isotope, they were stimulated tetanically for 7.7 sec. One muscle of the pair remained isometric, the other one was slowly stretched. Some muscles were poisoned with fluorodinitrobenzene or dinitrophenol. The muscles were frozen rapidly after the last stimulus and phosphocreatine (PC), ATP and Pi were chemically analyzed. Phosphate isolated from these compounds was analyzed for 18O content by mass spectrometry. The water of the muscles is near the isotopic equilibrium with the water of the surrounding Ringer solution. Pi has a specific activity which is about one-quarter to one-fifth of that of water. This indicates that Pi split from PC or ATP is not recycled during the tetanus. PC has a specific activity which is about 90% of that of Pi. ATP has a specific activity much lower than that of Pi or PC. This is explained by the fact that both the terminal phosphates of ATP were used for isotopic analysis. If one assumes that ATP-Pi is in isotopic equilibrium with PC, then ATP-PB has a specific activity which is about one-third of that of Pi. Pre-treatment of the muscles with FDNB does not influence the specific activities of Pi or ATP; that of PC is however very low. This indicates that the Lohmann reaction is the only path which involves PC. Stretch does not change 18O specific activity of Pi, ATP or PC. However, no conclusions can be drawn, because these compounds are so close to isotopic equilibrium. Stretched muscles use less ATP or PC than their isometric control. The ratio of the negative work received by the muscles to the amount of spared ~P was 8.7 kcal/mole for unpoisoned muscles and 25 kcal/mole for fluorodinitrobenzene-treated muscles. Estimation of this ratio was not possible for the muscles poisoned with dinitrophenol. Thus the experiment yielded no decision as to whether work imposed upon contracting muscle causes a synthesis of ATP or an inhibition of its breakdown. They did, however, yield detailed information on other aspects of the sparing of metabolism by negative work.
Citations
Maréchal, G., Mommaerts, W. F. M. H., & Seraydarian, K. (1974). The exchange of 18O between water and phosphate compounds in isolated frog sartorius muscle under conditions of negative work. Journal of mechanochemistry & cell motility, 3(1), 39-54. https://hdl.handle.net/2078.5/214621 (Original work published 1974)