Adaptive responses to chronic creatine loading (CL) and voluntary running (Run) in rat skeletal muscle

Abstract

We investigated whether CL and Run alters myosin heavy chain (MHC) based fibre types, the proteins that regulate intracellular calcium and the metabolic profile in the rat plantaris. Forty Sprague-Dawley male rats were assigned to one of four groups: CL+Sedentary (Cre-Sed); CL+Run (Cre-Run); control+Sed (Con-Sed); Con+Run (Con-Run). Cre-Run resulted in a 10% increase in type IIB fibres and a corresponding 11% decrease in type IIA fibres compared to Con-Run (P<0.03). Parvalbumin content was decreased by 75% in Cre-Sed and Cre-Run (P<0.04). No differences were observed in the fast Ca2+ ATPase isoform, SERCA1, in any of the groups (P>0.49). SERCA2 content, a slow Ca2+ ATPase isoform, was 21% and 19% lower in Cre-Sed and Cre-Run compared to Con-Sed and Con-Run, respectively (P≤0.05). Run increased citrate synthase and 3-hydroxyacyl-CoA dehydrogenase activities (P≤0.05), while phosphofructokinase and glyceraldehyde phosphate dehydrogenase activities did not change; Cr did not alter any of these enzyme contents (P>0.28). We conclude that CL during Run was able to maintain a faster fibre type while not changing the metabolic profile indicating a disconnect between coordinated fibre type conversions and metabolic phenotypic profiles. We suggest that CL alleviates the need for parvalbumin and SERCA2 expression probably due to enhanced high energy phosphate shuttling that better supports SERCA1. NSERC & AHFMR.