期刊
JOURNAL OF PHYSIOLOGY-LONDON
卷 535, 期 3, 页码 901-928出版社
WILEY
DOI: 10.1111/j.1469-7793.2001.00901.x
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1. In ischaemic exercise ATP is supplied only by glycogenolysis and net splitting of phosphocreatine (PCr). Furthermore, 'proton balance' involves only glycolytic lactate/H+ generation and net H+ 'consumption' by PCr splitting. This work examines the interplay between these, metabolic regulation and the creatine kinase equilibrium. 2. Nine male subjects (age 25-45 years) performed finger flexion (7 % maximal voluntary contraction at 0.67 Hz) under cuff ischaemia. P-31 magnetic resonance spectra were acquired from finger flexor muscle in a 4.7 T magnet using a 5 cm surface coil. 3. Initial PCr depletion rate estimates total ATP turnover rate; glycolytic ATP synthesis was obtained from this and changes in [PCr], and then used to obtain flux through 'distal' glycolysis (phosphofructokinase and beyond) to lactate; 'proximal' flux (through phosphorylase) vas obtained from this and changes in [phosphomonoester]. Total H+ load (lactate load less H+ consumption) was used to estimate cytosolic buffer capacity (beta). 4. Glycolytic ATP synthesis increased from near zero while PCr splitting declined. Net H+ load was approximately linear with pH, suggesting beta = 20 mmol 1(-1) (pH unit)(-1) at rest, increasing as pH falls. 5. Relationships between glycolytic rate and changes in [PCr] (i.e. the time-integrated mismatch between ATP use and production), and thus also [P-i] (substrate for phosphorylase), suggest that increase in glycolysis is due partly to 'open-loop' Ca2+-dependent conversion of phosphorylase b to a, and partly to the 'closed loop' increase in P-i consequent on net PCr splitting. 6. The 'settings' of these mechanisms have a strong influence on changes in pH and metabolite concentrations.
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