title: Metabolic and sarcoplasmic reticulum Ca2+ cycling responses in human muscle 4 days following prolonged exercise.
abstract: This study investigated the effects of prolonged exercise on muscle sarcoplasmic reticulum (SR) Ca2+ cycling properties and the metabolic responses with and without a session of exercise designed to reduce muscle glycogen reserves while on a normal carbohydrate (CHO) diet. Eight untrained males (VO(2peak) = 3.81 +/- 0.12 L/min, mean +/- SE) performed a standardized cycle-to-fatigue at 55% VO(2peak) while on a normal CHO diet (Norm CHO) and 4 days following prolonged exercise while on a normal CHO diet (Ex+Norm CHO). Compared to rest, exercise in Norm CHO to fatigue resulted in significant reductions (p < 0.05) in Ca2+ uptake (3.17 +/- 0.21 vs. 2.47 +/- 0.12 micromol.(g protein)-1.min-1), maximal Ca2+ ATPase activity (Vmax, 152 +/- 12 vs. 119 +/- 9 micromol.(g protein)-1.min-1) and both phase 1 (15.1 +/- 0.98 vs. 13.1 +/- 0.28 micromol.(g protein)-1.min-1) and phase 2 (6.56 +/- 0.33 vs. 4.91 +/- 0.28 micromol.(g protein)-1.min-1) Ca2+ release in vastus lateralis muscle. No differences were observed between Norm CHO and Ex-Norm CHO in the response of these properties to exercise. Compared with Norm CHO, Ex+Norm CHO resulted in higher (p < 0.05) resting Ca2+ uptake (3.17 +/- 0.21 vs. 3.49 +/- 0.24 micromol.(g protein).min-1 and higher ionophore ratio, defined as the ratio of Vmax measured with and without the Ca2+-ionophore A23187, (2.3 +/- 0.3 vs. 4.4 +/- 0.3 micromol.(g protein).min-1) at fatigue. No differences were observed between conditions in the concentration of muscle glycogen, the high-energy phosphates (ATP and PCr), or metabolites (Pi, Cr, and lactate). Ex+Norm CHO also failed to modify the exercise-induced changes in CHO and fat oxidation. We conclude that prolonged exercise to fatigue performed 4 days following glycogen-depleting exercise while on a normal CHO diet elevates resting Ca2+ uptake and prevents increases in SR membrane permeability to Ca2+ as measured by the ionophore ratio.
authors.affiliation: Department of Kinesiology, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada.
authors.forename: T A
authors.initials: TA
authors.lastname: Duhamel
authors.forename: H J
authors.initials: HJ
authors.lastname: Green
authors.forename: J G
authors.initials: JG
authors.lastname: Perco
authors.forename: J
authors.initials: J
authors.lastname: Ouyang
mesh_terms: D000328:Adult; D015308:Anaerobic Threshold / Q000502:physiology; D001786:Blood Glucose / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D004032:Diet; D004040:Dietary Carbohydrates / Q000494:pharmacology; D015444:Exercise / Q000502:physiology*; D006003:Glycogen / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology; D018482:Muscle, Skeletal / Q000378:metabolism*; D010084:Oxidation-Reduction; D010101:Oxygen Consumption / Q000502:physiology; D011659:Pulmonary Gas Exchange / Q000502:physiology; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*
chemical_list: D001786:Blood Glucose; D004040:Dietary Carbohydrates; D006003:Glycogen; D000252:Calcium-Transporting ATPases; D002118:Calcium