The molecular regulation of exercised-induced muscle fibre hypertrophy in the common carp: Expression of MyoD, PCNA and components of the calcineurin-signalling pathway

Abstract

Growth was investigated over 16 d in juvenile common carp ( Cyprinus carpio L.) held in either static water (tank rested, TR 16) or exercised in a flume at 2.5–3.2 body lengths s − 1 for 18 h a day (exercised, E 16). Relative to the start of the experiment (TR 0), the TR 16 group showed a 31% increase in body mass (specific growth rate, 1.57% d − 1 ), whereas there was no net change in the E 16 group. There was, however, a significant exercise-induced hypertrophy of slow muscle fibres with average fibre cross-sectional area ( F CSA) increasing by 35% in the E 16 group, compared with 11% in the TR 16 group. In contrast, F CSA of fast muscle fibres increased by 34% in the TR 16 group compared to just 18% in the E 16 group. The relative concentrations and subcellular localisation of proteins hypothesised to play a role in the regulation of muscle growth were measured. MyoD concentration was similar in the TR 0, TR 16 and E 16 groups in both slow and fast muscle. However, there was a small (5%–10%) but statistically significant increase in nuclear localisation of MyoD in those groups showing a significant increase in F CSA over the time course of the experiment. PCNA concentration was 31% and 12% higher in the TR 16 than in either the TR 0 or E 16 groups for slow and fast muscle, respectively. Exercise resulted in a ∼10% increase in nuclear factor of T-cells (NFAT2) concentration in slow muscle but no change in NFAT2 localisation. Calcineurin B concentration was similar in tank rested and exercised groups. The results do not support a major role for the calcineurin-signalling pathway in the regulation of muscle hypertrophy in the common carp.