Muscle ATP synthesis and utilisation, balanced during flow-induced increase of respiration

To investigate the control of cell energetic metabolism, creatine charge, ATP/ADP ratio and oxygen consumption (as indicators of an energetic status, the balance between ATP synthesis and degradation and the aerobic ATP turnover, respectively) were evaluated in the rat gracilis muscle, perfused-superfused in vitro. During the perfusion rate of 70 microl/min the ATP/ADP ratio, as well as the creatine charge are kept at the in vivo level. With the decrease of the rate toward 54 microl/min (of an abundant oxygen delivery), the values of both parameters are lower than levels in vivo. With the increase of the rate up to 100 microl/min, both parameters are kept at the in vivo level, when respiration increases by 125%. The data demonstrate the 'unmatched' control of ATP utilisation and synthesis steady rates during the low perfusion rate; during the increasing steady ATP turnover following the increased perfusion rate, the two fluxes are strikingly 'matched', i.e. precisely balanced.