LAUSR

Eccentric (ECC) contractions-induced muscle damage is associated with calcium ion (Ca2+) influx from the extracellular milieu through stretch-activated channels. It remains unknown whether Ca2+influx consequent to repetitive ECC contractions is non-uniform across different muscle regions. We tested the hypothesis that there are regional differences in Ca2+entry along the proximal-middle-distal muscle axis. Tibialis anterior (TA) muscles of adult male Wistar rats were exposed by reflecting the overlying skin and fasciae and ECC contractions evoked by nerve stimulation paired with ankle extension (50 times/set, 2 protocols: 1 set and 10 sets). During ECC in the proximal, middle and distal TA we determined: 1. muscle fiber extension by high speed camera (200/sec), 2. Ca2+ accumulation by in vivobioimaging. Muscle fiber(s) extension from resting was significantly different among regions (i.e., proximal, 4.0%: < middle, 11.2%: < distal, 17.0%: ECC phase length at 500th contraction). Intracellular Ca2+ accumulation after 1 set of ECC was highest in the distal than the proximal or middle regions. However, this regional Ca2+ accumulation difference disappeared by 32.5 minutes after 1 set protocol when the muscle was quiescent and by contractions set 5 for the 10 sets protocol. The initial preferential ECC-induced Ca2+ accumulation observed distally was associated spatially with the greater muscle extension compared with that of the proximal and middle regions. Disappearance of the regional Ca2+accumulation in quiescent and ECC-contracting muscle might be explained, in part, by axial Ca2+propagation and account for the uniformity of muscle damage across regions evident 3 days post-ECC.