Early detection of severe complications of overstrenous exercise is important for athletes undertaking unaccustomed training. SCN5A gene plays a key role in encoding integral protein and
tetrodotoxn-insensitive sodium channel. The blood SCN5A mRNA level, which is sensitive to muscle contraction and metabolism requirements, reflects cell excitability. In this study, the dynamic
alterations of blood SCN5A mRNA level was investigated and compared with other biomarkers in response to repetitive unaccustomed exercise.
Thirty six male Wistar rats (320±10 g) were divided into the sedentary group (S, n= 6) and the overtraining group (OT, n= 30). Rats ran to exhaustion twice a day for ten consecutive days. Blood
samples were collected daily pre-, and post- (1- & 12-h) exercise. Two OT rats were sacrificed 12 hours after running in each day. The S and remaining 10 OT rats were killed after the final session.
The OT rats showed malaise, poor grooming, rough hair coat, and anorexia. At the end of the training session, the body weight, the weight of perirenal fat pad and the volume of forearm muscle of the
OT rats decreased by 22% (P < 0.01), 60% (P < 0.05) and 44% (P < 0.01) respectively, compared with S. The exhaustion time of OT rats declined progressively during the exercise training session (day
2-3 vs. day 1: -40%, P < 0.01; day 10 vs. day 3: -11%, P < 0.05). Histology found focal necrosis in liver and skeletal muscle after 4 days of running. Compared with the pre-exercise state of the 1st
day, an increased level of serum alanine aminotransferase was detected on day 1-10(P<0.05), creatine kinase on day 3-10 (P<0.05), cardiac troponin I on day 5(P<0.05), at 12h post-exercise time point
respectively. However, blood SCN5A mRNA level decreased on day 1-10 at 12h time point, compared with the pre-exercise state of the 1st day (P < 0.01). Whereas it increased on day 1-8 at 1h
post-exercise time point compared with pre-exercise state of the same day (P < 0.01).
The elevation of SCN5A mRNA in response to acute stressors is important in ensuring more protein expression for assembly sodium channel. As stimulation lasts, SCN5A expression can be inhibited to
limit cell excitability. In this study, SCN5A mRNA level was dynamically changed during different training periods reflecting the cell adaptation in response to repetitive unaccustomed exercise.
Combined with histology and biochemical measurements, blood SCN5A mRNA level can be used as an early indicator for overtraining monitoring.