title: Effects of prior exercise and a low-carbohydrate diet on muscle sarcoplasmic reticulum function during cycling in women.
abstract: The effects of exercise and diet on sarcoplasmic reticulum Ca(2+)-cycling properties in female vastus lateralis muscle were investigated in two groups of women following four different conditions. The conditions were 4 days of a low-carbohydrate (Lo CHO) and glycogen-depleting exercise plus a Lo CHO diet (Ex + Lo CHO) (experiment 2) and 4 days of normal CHO (Norm CHO) and glycogen-depleting exercise plus Norm CHO (Ex + Norm CHO) (experiment 1). Peak aerobic power (Vo2peak)) was 38.1 +/- 1.4 (SE); n = 9 and 35.6 +/- 1.4 ml.kg(-1).min(-1); n = 9, respectively. Sarcoplasmic reticulum properties measured in vitro in homogenates (micromol.g protein(-1).min(-1)) indicated exercise-induced reductions (P < 0.05) in maximal Ca(2+)-ATPase activity (0 > 30, 60 min > fatigue), Ca(2+) uptake (0 > 30 > 60 min, fatigue), and Ca(2+) release, both phase 1 (0, 30 > 60 min, fatigue) and phase 2 (0 > 30, 60 min, fatigue; 30 min > fatigue) in Norm CHO. Exercise was without effect in altering the Hill slope (n(H)), defined as the slope of relationship between Ca(2+)-ATPase activity and Ca(2+) concentration. No differences were observed between Norm CHO and Ex+Norm CHO. Compared with Norm CHO, Lo CHO resulted in a lower (P < 0.05) Ca(2+) uptake, phase 1 Ca(2+) release (30 min), and n(H). Ex + Lo CHO resulted in a greater (P < 0.05) Ca(2+) uptake and n(H) compared with Lo CHO. The results demonstrate that Lo CHO alone can disrupt SR Ca(2+) cycling and that, with the exception of Ca(2+) release, a glycogen-depleting session of exercise before Lo CHO can reverse the effects.
authors.affiliation: Dept. of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1.
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: D000222:Adaptation, Physiological / Q000502:physiology; D000328:Adult; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D004040:Dietary Carbohydrates / Q000378:metabolism*; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D005260:Female; D006801:Humans; D018482:Muscle, Skeletal / Q000502:physiology*; D010807:Physical Endurance / Q000502:physiology*; D012519:Sarcoplasmic Reticulum / Q000502:physiology*
chemical_list: D004040:Dietary Carbohydrates; D002118:Calcium