title: Regulation of oxidative and glycogenolytic ATP synthesis in exercising rat skeletal muscle studied by 31P magnetic resonance spectroscopy.
abstract: 31P magnetic resonance spectroscopy measurements of pH and the concentrations of orthophosphate and phosphocreatine were used to estimate rates of glycogenolytic and oxidative ATP synthesis in rat leg muscle during 6 min sciatic nerve stimulation at different rates (1-4 Hz). To study the regulation of glycogenolysis during exercise, the apparent 'glycogenolytic capacity' (L(MAX)) was calculated from glycogenolytic ATP synthesis rate and orthophosphate concentration as a measure of the Ca2+-dependent activation of glycogen phosphorylase. This was found to be proportional to the total ATP synthesis rate (F), and to decline with time; expressed relative to total ATP turnover rate as L(MAX)/F, its initial value was 2.9+/-0.6, declining with half-time 1.4+/-0.4 min. The apparent 'mitochondrial capacity' (Q(MAX)), calculated from oxidative ATP synthesis rate and [ADP], was independent of ATP turnover rate, but increased with half-time 0.8+/-0.1 min to 29+/-2 mmol kg(-1) min(-1): thus [ADP] was the predominant but not the only influence on oxidative ATP synthesis. Numerical simulation shows that time-dependent changes in L(MAX)/F exert a strong influence on pH and on the concentrations of phosphocreatine and ADP.
authors.affiliation: MRC Biochemical and Clinical Magnetic Resonance Unit, Oxford Radcliffe Hospital, UK.
authors.forename: G J
authors.initials: GJ
authors.lastname: Kemp
authors.forename: A L
authors.initials: AL
authors.lastname: Sanderson
authors.forename: C H
authors.initials: CH
authors.lastname: Thompson
authors.forename: G K
authors.initials: GK
authors.lastname: Radda
mesh_terms: D000255:Adenosine Triphosphate / Q000096:biosynthesis*; D000818:Animals; D004558:Electric Stimulation; D006003:Glycogen / Q000378:metabolism*; D016014:Linear Models; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000294:innervation / Q000378:metabolism* / Q000473:pathology; D010084:Oxidation-Reduction; D010725:Phosphocreatine / Q000378:metabolism; D010758:Phosphorus; D005082:Physical Exertion / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D012584:Sciatic Nerve / Q000502:physiology
chemical_list: D010725:Phosphocreatine; D010758:Phosphorus; D000255:Adenosine Triphosphate; D006003:Glycogen