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Interrelations of ATP synthesis and proton handling in ischaemically exercising human forearm muscle studied by 31 P magnetic resonance spectroscopy
Author(s) -
Kemp Graham J.,
Roussel Magali,
Bendahan David,
Fur Yann Le,
Cozzone Patrick J.
Publication year - 2001
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.2001.00901.x
Subject(s) - glycolysis , phosphofructokinase , glycogen phosphorylase , phosphocreatine , chemistry , medicine , anaerobic glycolysis , creatine kinase , nuclear magnetic resonance , endocrinology , biophysics , biochemistry , metabolism , biology , enzyme , physics , energy metabolism
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. 31 P 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) was obtained from this and changes in [phosphomonoester]. Total H + load (lactate load less H + consumption) was used to estimate cytosolic buffer capacity (β). 4 Glycolytic ATP synthesis increased from near zero while PCr splitting declined. Net H + load was approximately linear with pH, suggesting β= 20 mmol l −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’ Ca 2+ ‐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.