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 Ca2+-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 (V̇o2peak) 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 (μmol·g protein−1·min−1) indicated exercise-induced reductions ( P < 0.05) in maximal Ca2+-ATPase activity (0 > 30, 60 min > fatigue), Ca2+uptake (0 > 30 > 60 min, fatigue), and Ca2+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 ( nH), defined as the slope of relationship between Ca2+-ATPase activity and Ca2+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) Ca2+uptake, phase 1 Ca2+release (30 min), and nH. Ex + Lo CHO resulted in a greater ( P < 0.05) Ca2+uptake and nHcompared with Lo CHO. The results demonstrate that Lo CHO alone can disrupt SR Ca2+cycling and that, with the exception of Ca2+release, a glycogen-depleting session of exercise before Lo CHO can reverse the effects.